Embryogenesis: Theory, Principles and Application

Articles

Embryogenesis: Theory, Principles and Application

With Annotated Bibliography

Michael J. Shea, PhD 2010

Introduction

It can be said that we now live in the era of the embryo. It is on the front page of newspapers and magazines around the world regularly. The human embryo has become a politician, a Christian, a researcher, a healer and at last a human being in the last decade. I remember the summer before 9-11 happened. Then President Bush was making a decision about the U.S. government’s role in stem cell research.

The front page of the USA Today newspaper had color pictures of multiple stages of the human embryo in its first week of development covering the story about the president’s upcoming decision. I knew then and have had it verified a hundred times since, that the embryo was front and center in the psyche and consciousness not just of Americans but of the whole planet. Many countries are now in the business of stem cell research, cloning research, using assisted reproductive technologies (ART), debating abortion rights and various interpretations of the Judeo-Christian creation story found in the book of Genesis in the Bible.

I cannot provide images of the embryo in this article but I have included a comprehensive list of books and websites that are full of images at the end of this article. I recommend Ulrich Drew’s book from that list (#8) called Color Atlas and Textbook of Human Embryology. It is important to look at images of human embryos while reading this article. I want to help the reader understand a few principles of embryology that apply to any pre and perinatal practice. That understanding is amplified by seeing images of the actual embryo. Here are some basic principles to explore in order to navigate the contemporary human embryo.

Phylogeny Does Not Recapitulate Ontogeny

In the eighteenth century a scientist by the name of Ernst Haeckel believed he saw vestiges of animal structures in the human embryo such as a tail, fins and gills like a fish. The human embryo however has no gills, no tail, and no fins or other amphibian or reptilian vestiges of evolutionary development. One could state that there are gill-LIKE or tail-LIKE structures in the human embryo, but morphological homology (a similarity to its final characteristic in development) between species does not prove that we have those SAME structures and functions!

This is a complete reversal of Haeckel’s Biogenic Law from the nineteenth century that states: ontogeny recapitulates phylogeny. This theory persisted for over one hundred years in the field of human embryology. Ontogeny, the development of the human embryo, clearly and emphatically does not recapitulate phylogeny, the evolutionary development of our species. All of our ancestral remnants seem to be located as spare parts in the human genome buried as strands of DNA among those genes that are uniquely human. The more the genome is studied the smaller the amount of genes that belong to us. Moreover we have now learned from the HUGO project that biological humanness is not IN the genes but located in the epigenetic process in which the genes are regulated (switched on and off, activated in a given order of time called sequencing in relationship to the movement of the cytoplasm in the cell and the shape of the cell membrane as it is influenced by extra-cellular movements) which determines the specific outcome of the embryonic development. I will cover epigenesis further ahead.

The human embryo in its early stages is almost invisible to the naked eye. It is very small and clear like glass. It is seemingly without structure. Therefore in order to see it, special staining and lighting techniques were needed and now ultrasound equipment is used. It is obvious from the early investigations of the German embryologist Dr. Erich Blechschmidt and current studies that the human embryo is not related to any other mammal in its structural appearance (E. Blechschmidt, 1977, 2004; E. Blechschmidt, Gasser, R. , 1978). This is true from the moment of conception. There may be similarities in appearance to other species but the cellular shapes, the timing of differentiations and the direction of cell fates are surprisingly quite different when one looks more closely at the human embryo.

As Dr. van der Wal, a Dutch embryologist, has said in his lectures (see his website listed at the end of this article) you can only learn about the human embryo by studying the human embryo. Most embryology books from the 1950’s through the 1980’s were essentially comparative embryology texts that inferred much of human development from studying other species. Consequently, names were given to human embryo functions and structures that turn out are not really there in the same way as they are in other species. Limited numbers of human embryos were available for study and competition among universities was intense. A good example of this is the yolk sack of a chick embryo which is quite different than a human. Yet the name yolk sack persists in many books as a descriptor of the human umbilical vesicle. Finally in 2010 the international embryological nomenclature committee approved a complete revision of the elements of the embryo.

Adult Function is Pre-Exercised in the Embryo

All present functions in the adult body are already in place in the early embryo. In other words, all adult function is pre-exercised in the embryo. Breathing is a good example. At conception the embryo begins to make a movement that Dr. Blechschmidt called a suction field (think of the bellows used at fire places to blow air onto the fire). It is a reciprocal tension fluid movement like inhalation and exhalation found throughout the fluid structure of the embryo. He surmised that this was a prelude to the function of the lungs. Later on in the embryonic development a similar ‘suction field’ transforms the lung vesicle protruding from the primitive foregut into an inspiring lung field filling the retrocardial space in the thoracic cavity. It appears to be breathing in and out by the very fact of its growth.

Another example is the systemic circulation of blood in the periphery of the embryo. Blood forms outside of the body of the embryo proper around the chorionic cavity before a heart is present. The blood circulates under its own power and gradually makes connections to the center of the embryo and the heart several weeks later. Thus systemic circulation of blood in the adult body is pre-exercised in the embryo, since the adult heart cannot be the cause of such circulation in the capillary beds as far away as the lower legs for example. In other words function precedes structure. Precedes does not simply mean that function precedes structure in time although it frequently does. Here this principle indicates more of the hierarchical relationship that exists between function and structure. One could also state that function and structure are BOTH the expression of function. It is a hierarchically higher functional principle or functional field.

The embryo thus solves the which came first, the chicken or the egg? problem. Considered in this way, the embryo exhibits behavior: form as function and as biological behavior. This is a very important consideration therapeutically. The DSM-V (diagnostic and statistical manual of mental disorders) provides a description of the structure of a neurosis or psychosis. Yet, one must face a client in the totality of their humanness and how they are functioning in life. Thus a possible starting point for a therapeutic relationship is the felt sense of wholeness in the therapist and the therapist’s ability in seeing and sensing the wholeness of the client. And consequently the client knowing he or she is being seen in this way.

The Tempo of Healing

The archaic stages of culture and initiation include a series of rites whose symbolism is crystal clear: through them, the novice is first transformed into an embryo and then is reborn. Initiation is equivalent to a second birth. It is through the agency of initiation that one becomes both a socially responsible and culturally awakened being. The return to the womb is signified…by entering a sacred spot identified with the uterus of mother earth…the basic idea is that, to attain a higher mode of existence, gestation and birth must be repeated; but they are repeated ritually, symbolically (Eliade, 1963, pp. 79-82).

There are several important reasons for studying the embryo beyond the scientific. One reason is about cultural healing. Healing, which is different but related to a therapeutic process, fundamentally involves what Eliade (1958, 1963) calls a "return to origins" or regressum ad uterum. One must experience their original wholeness symbolically (perhaps at church or via psychotherapy or manual therapy). The symbol that I experience most frequently in my clinical practice is the conscious awareness of stillness and a slow tempo in myself first and then the client. According to the experience of some clinicians, this causes a reorientation to one’s origin as it was in the beginning at conception. This occurs in present time for the therapist and the client. It is not a hypnotic retrieval of prenatal experience. Rather it is the complete normalization of one’s experience by linking it to a slow tempo and a dynamic stillness free of dissociative affect. This tempo and orientation to a dynamic alive stillness and a slow tempo was present throughout the embryonic period (fertilization through 8-10 weeks) as a force of growth and development according to some embryologists. Throughout this article I will be focusing on how to apply stillness and a slow tempo in a therapeutic relationship.

The medicine people in preliterate cultures knew this principle and healing rituals were designed to give patients this experience because disease was a spiritual problem. The patient could not be fixed. The patient had to start all over again at the beginning of his or her conception or in some cultures at the beginning of the universe. This was the time when each person was whole as a single-celled human body. Perhaps the debate about intelligent design of the embryo being played out in the political arena is precisely this need of the psyche to touch its origins for healing. At the same time, the Hubble Space Telescope keeps delivering new pictures of galaxies that formed right after the Big Bang. Images of our origins are constantly in our faces.

As the exemplary model for all "creation," the cosmogonic myth can help the patient to make a "new beginning" of his life. The return to origins gives the hope of rebirth. Now all the medical rituals we have been examining aim at a return to origins. We get the impression that for archaic societies life cannot be repaired; it can only be re-created by a return to sources. And the "source of sources" is the prodigious outpouring of energy, life, and fecundity that occurred at the Creation of the World (Eliade, 1958, p. 30).

I associate a slow tempo and stillness to Eliade’s notion of "energy, life and fecundity." Embryology is the new anatomy, because when one touches another person one has their hands on more embryology than they do anatomy and physiology. In other words, an adult body has an enormous potential for change and transformation. This includes change process in the mind and emotions as well because their foundation lies in the biology of the body. Almost every ten minutes during the embryonic period, the structure and function of the embryo disintegrates a pre-existing structure and starts to build a new one. This capacity is carried forward throughout life.

The therapeutic relationship is a two-person biology, just as it was in the womb (D. J. Siegel, 1999). The helping supportive relationship, similar to that of a mother and her newborn baby, works best if the mother (or the therapist) can access a slow tempo and stillness in herself or himself. The story of the human embryo is the new creation story because a slow tempo and stillness are viewed as the most formative shaping and ordering forces in the embryo by some embryologists and thus symbolic of our original wholeness as a living shape conserved over an entire lifetime. Biologists have said this for over a century that the wholeness observed in the embryo is carried forward throughout the life span in every single stage of growth and development. The movement of a slow tempo when coupled with the conscious awareness of a dynamic stillness are sensory perceptions available in and around adult bodies.

Wholeness

The embryo is also symbolic of wholeness because it always configures itself into a circle either through spiral movement in its fluids or the way its structure appears in every phase of its growth. "The circle represents God and eternity, wholeness and fulfillment of the transpersonal dimension of life. Being round in the initial period of existence is equivalent to assuming oneself to be total and complete and hence a god that can do all things" (Edinger, 1992, p. 8). The embryo itself is thus an image of wholeness spiritually and psychologically as much as a biological whole.

The embryo is a functioning whole according to embryologists in the 20th century. The German embryologist Dr. Eric Blechschmidt pointed out what he called the "originality" of embryonic human beings which is synonymous with biological wholeness. He said that this originality is discernible in many ways; for example, that the early human conceptus is master of its whole geometrical pattern of growth and development. Unless there is a noxious substance present, it is never mistaken about any position for its structural parts, and it is never deceived in any surface to volume ratio of its fluids and membranes. It never sets an organizing point or midline on the wrong site and is master of every physical, as well as cardiovascular reaction before a central nervous system is present. He said that "everyone could be enlightened from the abilities of the young embryo, but it is impossible to deduce its originality from scientific findings" (E. Blechschmidt, Gasser, R. , 1978, p. xiv).

The early embryo represents an originality and individuality from the moment of conception. And perhaps this is also true of the female egg which differentiated many years before when the mother herself was an embryo in her mother’s womb. It is a three dimensional wholeness, however, that is undifferentiated. The undifferentiated wholeness of the fertilized female egg is a single cell human body as mentioned. Wholeness is the first imprint for the later stages and complexity of differentiated wholeness of the human embryo, then the fetus, the child and, finally, the adult. "Man does not become man; he is man and behaves as such from the very commencement and in each phase of development from fertilization onward" (E. Blechschmidt, 1977, p. 17). The point I want to return to is that slow movement and stillness are a significant cause of embryonic wholeness.

The deeper forces initiating and maintaining human development are found in the fluids as a slow tempo and areas of stillness in the membrane wall because the embryo is all fluid. Then the blood develops and maintains a redundant system for wholeness in the second week post fertilization. Finally, in the fourth week the nervous system develops as a third management system of the experience of wholeness in the human body. Clinically, the contemporary client has a fragmented nervous system whether an infant or adult. This requires a therapist to orient to the preceding two systems of embryonic wholeness, the fluids and the blood-heart, to help the client back to an embodied wholeness. The therapist however must find his or her own fluid body and own heart and blood first. New research has shown that conscious attention on the movement of one’s heart builds empathy and changes the brain (Bechara, 2004).

The dynamic morphology of the embryo as it shapes itself constantly is an expression of a slow tempo. Embryonic motion and growth are viewed as sentient gestures or as Dr. van der Wal has said, the gesture is the "speech" of the embryo (Shea, 2007). Growth equals behavior which equals gesturing. The consciousness or sentience of the embryo is psychologically and spiritually expressing itself in the very movement patterns of its growth. The embryo is the visible gesture of the invisible act of incarnation and embodiment. In other words, the growing gesture is a form of unique psychological and spiritual expression from a phenomenological viewpoint (van der Wal, 2004).

Scientific studies of the human embryo count precisely twenty three stages or phases of structural and functional development before all major organ systems are finished with their basic construction and the embryo can be considered a fetus, the time of filling out. These are referred to as the Carnegie Stages in embryology books (O'Rahilly & Muller, 1987). The total time that these structural stages take to develop is about ten weeks. And almost every 10 minutes during that 10 weeks, structures disintegrate and new ones are formed. The tempo and precision of each stage is due to the continuity of wholeness carried by the biodynamic forces of a slow tempo and stillness acting to create order as the embryo becomes more and more complex. This order in the fluids spoken of by Dr. Blechschmidt is moving at a slow tempo. It feels like a slow breathing motion or a long tide coming in and out according to biodynamic craniosacral therapy practitioners and osteopaths.

It is not limited to the body alone but can be sensed around the body and out into nature. Have you ever been with a client and find yourself briefly staring out the window at a tree trunk? This is stillness outside. Have you ever been with a client and in a pause without talking a vibrating stillness fills the office? It is also located within the fluids and helps organize the metabolism of the embryo and adult. It is three dimensional. It preserves the unique wholeness of the embryo forward into the adult. Each structural stage is whole and complete because the embryo undergoes a metamorphosis in each stage. It becomes something new. It will construct a vascular system to support several stages and then disintegrate those structures as a new shape emerges in the following stage(s). As a therapist, I must learn to pay attention to the movement of my heart and the three dimensional shape of my body in order to sense these changes constantly occurring both in myself and in the client. Conception, therefore, is viewed as the next phase in a developmental process of inheriting wholeness rather than the start of a new life. The form created in one stage literally dies, and a new form is created in the next stage. Each stage is whole and invites the next stage into existence. As stated before it is always the whole that keeps the differentiating and potential genetic chaotic tendencies of the organs and the body parts and so forth in equilibrium. The whole is an equilibrium. Dr. Blechschmidt called this the Law of the Maintenance of Individuality. Obviously things can go wrong which I will now address.

Death

Maternal stress can easily imprint the genes of the embryo and even her eggs when she is an adolescent. The field of teratology describes defects in the embryo, fetus and infant that result from a noxious outside-in experience, whether it is a chemical like alcohol or the thought of having an abortion by the mother (Lewis & Cahalan, 1989; Normile, 1998). Many human embryos die, seemingly at random, without any known external or internal complications. As a matter of fact, more human embryos perish than any other species of mammals. The reasons for this are not clear scientifically although some evidence supports genetic defects in one or more of the omnipotent cells in the embryo during the first week post fertilization. In other words, as cells multiply in the first week before they divide into an inner cell mass (stem cells) and an outer cell mass, each of the cells in the embryo could individually become a complete human and are called totipotent or pluripotent. Now evidence shows that all these cells are not the same and some may be defective and cause the whole embryo to abort.

So, needless to say, the act of creation is precarious. What does this tell us about perfection and wholeness? To study the embryo is to study death. More human embryos perish than any other species as I said earlier. Thus the embryo is also the master of death and prepares itself from conception for its end, whether it happens soon after conception or many years later. Its preparation is its own fragility and reliance upon the uterine environment for life. Research has shown that 90% of all women experience prenatal loss through miscarriage, abortion or still birth (Peterson, 1994). Thus the uterus exists to hold death and life. I believe that death is one of the deepest imprints on embryonic existence next to love.

Creation myths and legends tell us that the divine seeks to create an image or pattern of itself in the natural world and, once this impulse, potential or image is conceived, again an equal or opposite or complementary force is generated like a mirror. This other force is death. It has been discovered that the majority of human conceptions involve the presence of a twin, many of whom perish within several weeks. Many embryos never come to term as I said above, so death, the complement and polarity of creation, is ever present as a potential. This is a consistent theme found in all creation mythologies, whether it is our Western motif of the human embryo or the Iroquois creation myth of the woman who fell from the sky (von Franz, 1995).

Artists especially know the difficulty of bringing a creative idea to fruition. The clarity of the original impulse, thought or sensation is constantly forged by the mind and body until, finally, a birth occurs or a death. A therapist can synchronize his or her attention with slowness and stillness in herself or himself and help balance the forces of life as a slow tempo and death as a stillness that is without fear. Fear takes the place of love. Death becomes an extremely important contemplation for therapists, not just physical death, but the death of a neurosis, a thought pattern or behavior in one’s self and another.

The Buddhists call this a contemplation on impermanence. Love and death are not individual affairs, but something common to everyone. Nor are they capable of being subdued by managed care. Thus, two polarities arise in the process of conception: one’s relationship to love and death. These forces exist within the embryo — love and death — and are present at all times. This is also an aspect of wholeness. Thus the embryo is the unitary symbol of the wholeness and order inherent on the planet. Late in his life Carl Jung said that the psyche is extinguished in the body’s materiality. What this meant to him is that in the symbol of the body the entire cosmos is speaking. This is how and why the human embryo speaks to us now in our very post modern world, as a symbol of love and death. Remember the political discourse on stem cell research that requires killing human embryos to harvest stem cells.

Morphology

Morphology is the study of the physical movement and shaping of the human embryo as a fluid body being shaped by its internal and external environment. It is classically defined as having four stages: Stage one corresponds to week one post fertilization, stage two is week two, stage three is week three and stage four comprises weeks four through eight which is the end of the embryonic period. These stages are quite different than the Carnegie stages mentioned earlier. Morphology includes the sense of the totality of all structure and function in the embryo, which includes its relationships with another person, specifically the mother and her nervous and cardiovascular systems.

This has great implications for clinical practice with adults as adult relationships involve interpersonal nervous systems (D. Siegel, 2010). Thus the therapeutic relationship is a dynamic morphology being constantly shaped moment to moment through the process of intersubjectivity (Stern, 2004). And morphology as an expression of continuous self regulation includes the autonomous growth and development of the embryo dynamically in balance with the uterus and mother. Morphology is a domain of body knowledge and sensibility. It describes how to pay attention to one’s body, especially in a therapeutic relationship. It requires at the very least becoming consciously aware of the entire three dimensional surface of one’s body as a single shaping process. This type of conscious bodily knowing is called interoceptive awareness (Critchley, Wiens, Rotshtein, Ohman, & Dolan, 2004). Specific strategies are then employed to help the therapist and the client to maintain such awareness such as conscious breathing or using a body scan from head to foot.

The four stages of dynamic morphology correspond to significant growth movements in the embryo that reoccur throughout the life span. Each stage demands a lot of energy to transition from one to the other, otherwise death will result. During the first week of development, the dominant movement is one of compression. The relative size of the embryo does not change. Rather, the pluripotent cells on the inside must become compressed and smaller in order to accommodate an unchanging shape. The first week being dominated by compression is said to express the initial development of in internal world. This is because at the end of the first week, all the compression causes a fluid cavity to arise which will then become the yolk sac (umbilical vesicle). It is associated not only with the entire gastrointestinal system, but also the heart and blood. The first week is about the development of an internal world which will then become these two internal systems much later on in development.

The second week or stage of morphology has its dominant expression in expansion. It is completely the opposite of the first week. As a matter of fact, oncology experts study this second week because the embryo behaves as a cancer with its unrestrained growth. This unrestrained growth makes a connection with the outer world of the uterus and future placenta. So the morphological gesture of the second week is the development of an external world to support the embryo. I will speak more about this process later on under the heading of "Two Bodies".

The third week and stage of morphological development is concerned with the development of a middle. This is the space in between the inner and outer worlds from the first two weeks. The middle in this case is not only the future spine, but in particular the heart itself. The heart becomes the middle of our embryonic existence during the third week and remains so for the balance of the embryonic time and perhaps life.

The fourth stage of development comprising weeks 4 through 8 is dominated by the movement expressing folding and unfolding. Folding involves a bowing motion where the top of the head or neural tube at this stage curls forward in order to make a better connection with the heart. Many images of the embryo show a form that is almost perfectly circular as mentioned earlier. Following this phase of folding over, the embryo unfolds itself towards its future upright position. It begins to lift its head up. To review, stage one involves compression and the development of an internal world. Stage two is about expansion and the development of an external world. Stage three is about the middle, balance and the heart. Stage four is about the basic gesture of folding, which appears to be the gesture of humility, and unfolding, which appears to be the gesture of freedom, which I will speak to later on.

There is a very specific application of this information in the therapeutic relationship. The principle involved here is that anything that begins as metabolism in the embryo can become physiology in the infant and psychology in the adult. Compression of the first week can be seen in numerous psychological dynamics in clients, especially in the day and age of stress and trauma. Clients carry very compressed experiences. The very nature of the therapeutic relationship is about connecting with another person and establishing a reality check with the outside world, as in the second week. Thus the therapeutic relationship at this level of understanding could be considered embryonic. The third stage of finding the middle ground and the path in between the polarities of life is quite obvious. The embryo teaches us that you must have a spine to develop character (a back bone) and you must also have a heart to find the middle ground between the extremes of life with loving kindness and compassion.

Finally, it could be said that the fourth stage of folding and unfolding is the delicate balance between the necessity of going in, withdrawing from the world and taking refuge in one’s self periodically and then coming out and unfolding or being reborn into a right relationship with self, other and community. This takes place over the last four to ten weeks of embryonic development. Isn’t this the rhythm of life? How do you manage life’s transitions from one stage to another? Don’t they usually take a couple of months to sort out? Orienting to stillness and a slow tempo allows the compression of life to normalize through connecting to its original function in the embryo.

Womb – Heart

The intimate connection of a mother to her child, heart-to-heart while inutero, and the stress of the mother that translates through the placenta via the blood and heart, are tremendous modulators of embryonic activity. Clinically, I have observed that often the uterine environment is associated with the natural world as if it were an extended womb. In other words, the experience of the womb goes beyond the actual uterus and is connected to the heart, as the heart is also connected to family, community and the natural world. Being pregnant is the most natural part of the natural world! The natural world is also called the Great Mother by Eric Neumann (1955). I often sense this dynamic when I have my attention on my own heart and blood while in contact with the client. I notice how my heart will accelerate sometimes and how the blood in my whole body will pulsate with the client, especially under my hands where my skin meets the client’s skin with or without a layer of cloth in between. This frequently occurs without contact as well. This is because the therapeutic relationship becomes a two person interpersonal cardiovascular system. Ask any mother about her experience of sensing the first heartbeat of her embryo and she will usually report ecstasy.

The heart is a very remarkable embryonic organ. It needs a lot of space in which to grow and develop in the embryo. Consequently, when it starts to grow, there are no other organs present in the body cavity. In this way, it is very unrestrained in its basic capacity to expand. As the heart expands, it does something very remarkable, in that it turns itself upside down. The heart begins as two tubes next to one another that merge into a single tube except that the top of the tube is the future ventricles and the bottom of the tube is the future atria. Over the course of several weeks, the heart must turn itself upside down.

These basic gestures of the heart are carried forward throughout life. The first is the capacity of two hearts and vascular systems to merge into a single entity as demonstrated by the mother embryo/fetus relationship and the very internal relationship of the individual heart to itself, where the two become one. Paul Pearsall (2007) calls this phenomena "interpersonal cardiovascular systems".

As a therapist, I frequently notice my heart accelerating during moments of the therapeutic relationship. This is not only the felt sense of the interpersonal cardiovascular system, but also the way in which the heart seeks to expand its capacity and, in a sense, take on the heart of another person. Finally, it must be said that no one seems to make it through life without having their heart turned upside down. This is true in love relationships, family relationships and friendships, as well. The question is how to normalize this experience? It is with stillness and a slow tempo.

A basic principle of development is that any process that begins metabolically in the embryo becomes physiology in the infant and child and finally becomes psychological in the adult. Clients may be able to uncouple from their trauma and reorient to their experience as normal with stillness and a slow tempo. Normal would result in the client gaining a deeper understanding of the meaning of their experience and its connection to their entire life. No part gets left out, rather everything is included as a tapestry woven together. This is the promise of stillness and slowness.

Epigenesis

Two basic theories of development dominate the field of human embryology. They are called morphology and epigenesis. Epigenesis historically meant that the form and development of an organism does not result directly from the action of the DNA and gene replication. Instead, it is due to deeper forces at work around the cell nucleus in the cytoplasm of the cell and the external environment that are mediated by the cell membrane (E. Blechschmidt, 1961; E. Blechschmidt, Gasser, R. , 1978; Hagmann, 1999; Maniatis, 1997; Pawson & Scott, 1997).

Forces in the cytoplasm and the environment outside the cell, as well as outside of the body, signal the genes to express and to be active. This happens specifically by the mechanical direction of movement (morphology) depending on the shape of the cell, the rhythm of the movement or what is called cellular convection in the cytoplasm. There are also molecular, electromagnetic and biochemical influences placed on the nucleus. Other forces from outside of the cell, called fluid fields, influence the construction of human form. All of these forces, especially the outside environment of the mother, have been little understood by the scientific community, until recently.

Epigenesis now specifically includes a layer of signaling molecules around the cell nucleus that can actually silence certain areas of the genome and usually in a negative way (Meaney, 2010). Epigenetic effects expressed as genetic alterations have been most recently researched and detected in the development of the early embryo and the placenta and are associated with maternal stress. The impact of the stressful maternal environment results in changes in gene transcription and the placenta goes into an inflammatory response which alters its structure and function and that of the fetus causing long term problems in the health of the individual (Relier, 2001; Wadhwa, 2005; Wadhwa et al., 2002).

The development of an organism, and the successive formation of its parts, is not preformed or exclusively dictated by genes, but equally includes morphology and environmental factors, especially stress. The forces directing the development of a human being, as a whole, are based on processes that are equally epigenetic and morphological. This does not negate or devalue the importance of genes. Genes are not the cause of body formation but are a necessary condition for it. Health then, at its deepest level is epigenetic. As Dr. Blechschmidt states, "The genes are not active, they are re-active in the process of differentiation which is a process from the ‘outside’ to the ‘inside’.

Dr. Blechschmidt said that the genetic structure is not "egotistical, it only tries to mediate between the old and the new." In other words, genes are not reproducible blueprints nor do they contain a functional design relationship between the DNA/RNA and the final organ characteristics. There is no constructional association dominated by the genes, such as between a color slide and its projection. There is no preformation in human development in terms of a human shape preexisting in miniature form in the genes. For each metamorphosis of the embryo, both developmental stimuli such as a slow tempo in the fluid fields of the cytoplasm (coming from outside in towards the cell nucleus) and gene expression are needed. Without genes there would be no center point of impact for the fluid forces. Without the fluid movement, the genes would remain ineffective.

Thus genes do not act, but they react as stated by Dr. Blechschmidt. Genes are not self emergent. They have no intrinsic ability to turn themselves on and off. Since genes cannot control their own expression, they cannot control the behavior of the cell. They reproduce proteins when told to do so by epigenetic processes, the movement of the cytoplasm and the shaping of the cell membrane from the influences of the extracellular environment (Lipton, 2005). Consequently, the environment outside the cell nucleus and around it is primary (Meaney, 2010; Nijhout, 1990; Travis, 2000). I am myself, thanks to, as well as or rather in spite of, my genes.

According to unpublished research from the Max Planck Institute in Germany, the adult body is 92% living fluid as opposed to the typical textbook figure of 65%. Cells are shaped and differentiate as a result of the interplay between the genetic (especially the epigenetic forces) and the external environment (uterus, mom and fluids). Differentiation is then a process in between the two polarities of genes (inner) and environment (outer). Both forces are there from the moment of conception and one does not derive from the other. This twin phenomenon of biological forces being present from the differentiation of the egg cell being carried and conserved forward in development, is wholeness. I like to think that this wholeness precedes such notions as incarnation and embodiment.

The intelligence of stillness and a slow tempo causes the whole fluid body to continue its process of morphology (continuously shaping and forming as mentioned earlier). It is the decisive factor causing the organism to differentiate (E. Blechschmidt, 1977) and to normalize stress. The performance forces of slowness and stillness within the fluids of the embryo keep it moving in the direction of wholeness even in the presence of toxicity. Wholeness is primary in terms of biology, whereas the formation of the parts of the body and stress are secondary. The prime directive, so to speak, of one’s biology is to maintain wholeness. Since a slow tempo and stillness maintain the wholeness of the embryo, they are considered to be sources of order for normalizing developmental processes.

Two Bodies

According to Dr. van der Wal (Shea, 2007), the embryo generates two bodies at the end of its first week of development. The first body is the peripheral body and the second body is the central body. The peripheral body is composed of the membranes of the embryonic cavities in touch with the uterus especially the chorion. Later it will become the placenta. This represents a field of function outside and around the structure of the central body. The peripheral body maintains visceral functions (such as liver and kidney). This occurs as a result of the central body projecting those functions out to the periphery prior to the actual body structure itself being formed in the central body. It is truly an ingenious design plan. Once the central body builds the internal structure for a liver or kidney for example, it will reintegrate those functions from the periphery back into the center or body proper.

The central body which will become the actual soma later on in week three as described above when the heart folds to become the middle of the embryo’s existence. During the early stages of embryonic development, the central body is an envelope consisting of two layers of cells. It has no middle in the form of body parts or viscera. This means that function precedes structure. It is important to repeat that the central body projects its function to the periphery until the structure is built to bring the function back in. Now the placenta will retain an independent endocrine system, nervous system and vascular system and thus establishes a type of resistance to giving back all of its function to the center (Huppertz, Burton, Cross, & Kingdom, 2006; Myatt, 2006; Pardi & Cetin, 2006).

The first job of the embryo is to build its cavities and external boundaries in order to hold itself and have a place to develop (Vogler, 1987). This is a natural process throughout life. First metabolic function is projected to the nearest body outside. Then, later in life, physiological function is projected out, as an infant does with his mother. Finally, throughout the lifespan, psychological function is projected out and onto other people until such time that it can be re-owned and re-integrated in the psyche of the projector. What starts as metabolic function in the embryo continues throughout life as a part of our basic nature as stated earlier. Anger is a classic example of an emotion typically projected onto other people especially loved ones and politicians. Gradually one’s anger must be tamed and owned. This requires making an internal structure neurologically that can witness and down regulate strong emotions (LeDoux, 2002; Schore, 2001, 2003).

It seems as if the embryo, in its growing and metamorphosing, performs the basic law of development: first you root in the periphery around you in order to find your impulses, instincts, and your nourishment and so forth. This provides you the conditions with which to build your own inner organization that, at birth, will reverse and development will become a resistance to this outward rooting process of the embryo. Being born is thus a gesture of de-veloping. At birth we en-velop or surround ourselves with a physiology of autonomy and relationship. The inner resistance of early growth and development mentioned earlier becomes an outer resistance after birth.

Conclusion: Resistance, Freedom and Normal

The embryo grows and moves with its metabolism against resistance which causes its unique differences in geometry, form and structure. There is no growth without resistance. This natural resistance is the real work of the metabolism of the embryo. The more it grows and becomes complex, the more resistance, both local and systemic, it must overcome in order to differentiate. There is resistance between adjacent structures and between fluids and membranes, between gradients of heat and different densities in the fluids. It is hard work being an embryo. Blechschmidt was fond of saying that proportionally, the embryo is working a thousand times harder metabolically than adult bodies are working. It is always running into resistance of some kind that it must overcome for survival and occasionally the resistance of the mother (Haig, 1996). So resistance must be considered to be part of the basic engine of life. It is normal but must not be overpowering to stifle growth or too weak in which coherency is lost. In this sense many embryos thrive on it and, as was said, some do not and die.

Natural growth resistance could be another reason so many embryos perish. Perhaps they just do not have the energy to continue especially at the end of each of the first three stages of morphology. Each stage of morphology requires a huge leap and reversal of direction in growth. The maintaining of a constant equilibrium against the forces of periphery and center, as Dr. Blechschmidt means in his Law of the Maintenance of Individuality, is already a permanent activity. The embryo is performing against resistance. Each organ is a performance not just a developing organism. For example, as the hands grow they come into resistance from the heart and this resistance causes the fingers and hands to form properly. Seen from the outside in photographs of the embryo, this development appears as if the embryo is embracing its heart. This is indeed a beautiful performance of an ancient dance.

At another level, the human embryo continually restrains itself from arriving at a final destination or specializing in terms of survival function like the rest of the animal kingdom does. It actively resists having animal features and always maintains itself as if an embryo throughout the lifespan. Moreover, according to Dr. van der Wal, it is true that on the level of self organization in the human embryo an opposite organizational principle seems to be active (valid) than is for animals. Where the animal actually strives for a functional and morphological adaptation and specialization, the human embryo on the contrary seems to continually restrain from specialization in an effort to keep up the more or less universal (archetypal) and original shapes and forms of its embryonic morphology. This allows the human being to develop his or her unlimited potential through the life span against the resistance of animal specialization (claws, fangs, a snout, etc.).

For the embryo, restraining is the performance against resistance par excellence. This leads to a morphology that opens up potencies in all directions: the morphology of freedom. Freedom here means the ability to transform one’s experience, to let go of one shape of behavior or belief quickly or over time. Human bodies and minds have this unlimited potential as a function of being mostly fluid. A case could be made biologically that the human retains more of its embryonic nature than other species throughout the lifespan. One teacher of mine said that humans are perpetual embryos. As a therapist I must sit in my own constantly changing body-mind process three dimensionally as I work with a client. My first teacher of embryology kept encouraging me to "find my embryo" and it took quite some time to do that exploration with my body. He knew when I had found my embryo because he could sense I finally loved my body without hesitation.

Healing requires a relationship to the ordering forces of stillness and a slow tempo to realize such transformation constantly available as a perceptual process in my body. This can lead to normalizing a person’s complete experience of life. This facilitates the morphology of freedom and the experience of becoming normal for both the therapist and the client. The forces of normalization and freedom are initiated by attunement to stillness and a slow tempo. They act as a catalyst and change experience through the body and consequently the mind. Becoming normal and having meaning is generated via a felt sense of wholeness in which every event in a person’s life makes sense. The shapes of health and healing are ever present in the body at this very moment. This is what the embryo teaches us. Acknowledgement This article was originally edited by Dr. Jaap van der Wal. I am very grateful for his most useful comments and additions to this way of being and way of thinking. In addition Dr. Ann Weinstein graciously and on short notice provided much needed editing assistance.

References

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Blechschmidt, E. (1977). The Beginnings of Human Life. New York: Springer-Verlag.

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Blechschmidt, E., Gasser, R. . (1978). Biokinetics and Biodynamics of Human Differentiation: Principles and Applications. Springfield, IL: Charles C. Thomas.

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Eliade, M. (1963). Myth and Reality. New York: Harper and Row.

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Myatt, L. (2006). Placental Adaptive Responses and Fetal Programming. Journal of Physiology, 572(1), 25-30.

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Pearsall, P. (2007). In Awe of the Heart. Alternative Therapies, 13(4), 16-19.

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Schore, A. N. (2003). Affect Regulation and the Repair of the Self. New York: W.W. Norton.

Shea, M. (2007). Craniosacral Therapy Volume One. Berkeley, CA: North Atlantic Books.

Siegel, D. (2010). Mindsight: The New Science of Personal Transformation. New York: Bantam.

Siegel, D. J. (1999). The Developing Mind: Toward a Neurobiology of Interpersonal Experience. New York: Guilford Press.

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van der Wal, J. (2004). Dynamic Morphology and Embryology. In G. van der Bie & M. Huber (Eds.), Foundations of Anthroposophical Medicine: A Training Manual (pp. 87-160). Edinburgh, Scotland: Floris Books.

Vogler, H. (1987). Human Blastogenesis: Formation of Extraembryonic Cavities. New York: Karger.

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Wadhwa, P. D., Glynn, L., Hobel, C. J., Garite, T. J., Porto, M., Chicz-DeMet, A., et al. (2002). Behavioral Perinatology: Biobehavioral Processes in Human Fetal Development. Regulatory Peptides, 108, 149-157. Annotated Bibliography of Human Embryology The following books, CDs and DVDs represent a cross section of texts, atlases and theories of human embryology having to do with molecular genetics, dynamic morphology and many beautiful embryological images. In general, Eric Blechschmidt, a great German embryologist of the past century, is credited with a thorough development of the morphological (wholistic) perspective in embryological research. His work is carried on in the United States by Dr. Raymond Gasser. These morphological principles form a core foundation for the practice and foundation of biodynamic craniosacral therapy.

1. Blechschmidt, E. (1961). The Stages of Human Development before Birth: An Introduction to Human Embryology. Philadelphia, PA: W. B. Saunders Company.
This is a fabulous atlas of black and white images. It is over 600 pages long and has both the German and English translation side by side. What makes it interesting, as well as with his other books, is the use of different types of symbols embedded in his drawings representing movement relationships, directions of movements and areas of restraint or stillness in the embryo. This allows the reader to generate a three dimensional sense of these movements in their own body.

2. Blechschmidt, E. (1977). The Beginnings of Human Life. New York: Springer Verlag.
This is the first text in English that Blechschmidt wrote. It is a short book and the best introduction to his work. This book introduces a set of images for the first time that show the movement and relationship of the eight metabolic fields in the fluid body of the embryo. As mentioned above, this gives the practitioner an opportunity to explore these possibilities within their own body as a three dimensional reality.

3. Blechschmidt, E. (2004). The Ontogenetic Basis of Human Anatomy: A Biodynamic Approach to Development from Conception to Birth. Brian Freeman (Trans.). Berkeley, CA: North Atlantic Books.
This book was published posthumously and edited by Brian Freeman. This is not an entry level text, but nonetheless is well edited and worthwhile reading with some background and familiarity with the embryo. The appendix is especially useful because the editor brings the reader up to date with very interesting embryological theory. Dr. Blechschmidt’s books must be accompanied by other embryology texts to help the reader fill in gaps in the information about specific structures and functions not covered.

4. Blechschmidt, E., Gasser, R. (1978). Biokinetics and Biodynamics of Human Differentiation: Principles and Applications. Springfield, IL: Charles C. Thomas.
This book is very popular in the osteopathic and craniosacral therapy professions. It is a very challenging book to read without some basic knowledge and understanding of the embryo. It is an advanced text. Dr. Gasser is still alive and Professor Emeritus at Louisiana State University in New Orleans. He currently has grants for a project called Digitally Reproduced Embryonic Morphology (DREM). This project of visually representing each stage of the human embryo is available through the website http://virtualhumanembryo.lsuhsc.edu/. In addition Dr. Gasser is working on a project disproving the theory of cell migration in the human embryo. He proposes that most embryology books only show surface growth, rather than differential rates of growth from a central organizing midline in the human embryo. For an excellent review of this work to date, please read Gasser, R. (2006). Evidence that Some Events of Mammalian Embryogenesis Can Result From Differential Growth, Making Migration Unnecessary.

5. Bogart, B. I., Ort, V. H. (2007). Elsevier’s Integrated Anatomy and Embryology. Philadelphia, PA: Mosby Elsevier.
I like this book because it is a new attempt to link embryology to the final adult anatomical form.

6. Carroll, S. B. (2005). Endless Forms Most Beautiful: The New Science of Evo Devo. New York: W. W. Norton & Company.
Dr. Carroll is a world renowned molecular biologist and entertaining writer. This is his first book introducing his metaphor of molecular genetics called Evo Devo. This first book is eminently readable and a must for the student of embryology.

7. Cochard, L. (2002). Netter’s Atlas of Human Embryology. Teterboro, NJ: Icon Learning Systems.
This atlas of human embryology has Frank Netter’s name on it, but many of the illustrations are done by several other illustrators. The principle author, Larry Cochard, acknowledges his teacher, David Langebartel, as being an invaluable mentor. Langebartel’s book is included in this reference list below.

8. Drews, U. (1993). Color Atlas of Human Embryology. New York: Thieme Medical Publishers.
This is my most favorite embryology text atlas. It is a small paperback, lavishly illustrated in beautiful colors. It is now available as a used book and very inexpensive. The second edition may be available at this time.

9. Gasser, G. (1975). Atlas of Human Embryos. Hagerstown, MD, Harper & Row.
This Atlas of Human Embryos was the first of its kind in the United States. This is because its orientation is morphological and the author is American. Dr. Gasser created an extensive library of precise drawings and illustrations that give the reader an incredibly accurate image of the embryo. Many atlases and textbooks of embryology only show the surface mass of the embryo growing which is not accurate. Dr. Gasser shows growth from a central reference point. This makes it a very accurate atlas of human embryology.

10. Gasser, R. (2009) Digitally Reproduced Embryonic Morphology, Stages 1-23. New Orleans, LA, Computer Imaging Laboratory, Cell Biology & Anatomy, LSU Health Sciences Center.
CDS and DVDs of the microscopic morphology and 3D reconstructions of the human embryo. The sectional morphology and 3D arrangement of the human embryo at all 23 developmental stages. The website is This email address is being protected from spambots. You need JavaScript enabled to view it. . for ordering information.

11. George, R. P., Tollefsen, C. (2008). Embryo: A Defense of Human Life. New York: Doubleday.
This is a new book by two philosophers, one from Princeton University and the other from the University of South Carolina. They argue for the wholeness of the human embryo as distinct from conception and link modern science with their philosophical argument.

12. Gilbert, S.G. (1989). Pictorial Human Embryology. Seattle, WA: University of Washington Press.
This is my most favorite atlas of embryological images. It is based on the original artwork done by illustrators of human embryology as far back as the 1920s. It is available as a used book through Amazon. I highly recommend it.

13. Grossinger, R. (2000). Embryogenesis: Species, Gender, and Identity. Berkeley, CA: North Atlantic Books.

14. Grossinger, R. (2003). Embryos, Galaxies, and Sentient Beings: How the Universe Makes Life. Berkeley, CA: North Atlantic Books.
These two books are huge and important. They are in depth explorations of the creation of life on this planet through the metaphor of embryology. This includes the various theories prevalent in science and mythology and more importantly, the consciousness of creation and the creative act. His information on embryology is solid and expansive requiring the reader to think and contemplate about life.

15. Haraway, D. J. (2004). Crystals, Fabrics, and Fields: Metaphors That Shape Embryos. Berkeley, CA: North Atlantic Books.
This is perhaps one of my most favorite books on the history of embryological theories. It is a reprint of Donna Haraway’s doctoral dissertation from Yale University. She discusses the three principle biologists of the 20th century that shaped the modern science of embryology.

16. Kirby, M. L. (2007). Cardiac Development. Oxford: Oxford University Press.
Margaret Kirby is the premier embryologist in the study of the development of the human heart. She is at Duke University and her website is http://kirbylab.mc.duke.edu/. She has excellent images and a PowerPoint presentation on the embryology of the heart available to download. Her book is the best written of the several texts available on heart development and follows a logical sequence for learning in depth about the human heart.

17. Konig, K. (2000). Embryology and World Evolution. London: Camphill Books.
Dr. Konig comes from a background in Rudolf Steiner’s work. This is a tiny little paperback that has an excellent and complete history of the study of human embryology starting with Aristotle. The second half of the book gets into Steiner’s theory on the relationship of astrology to embryology.

18. Langebartel, D.A. (1977). The Anatomical Primer: An Embryological Explanation of Human Gross Morphology. Baltimore: University Park Press.
This is one of the best books I’ve seen on the relationship of early embryological development to the final adult form. Each page has charming illustrations except that the only color used other than black and white is red. This also is available as a used book through Amazon. I highly recommend it because of its thoroughness and the use of light hearted cartoons to illustrate certain concepts.

19. Morgan, L. (2009). Icons of Life: A Cultural History of Human Embryos. Berkeley, CA: University of California Press.
This is a very interesting book on the history of the collection and study of human embryos in the United States.

20. Netter, F. (1978). The Ciba Collection of Medical Illustrations, Volume 5, A Compilation of Paintings on the Normal and Pathological Anatomy and Physiology, Embryology, and Diseases of the Heart. Summit, NJ: Ciba Pharmaceutical Company.
This book has a very good section on the embryology of the heart. Netter images are world famous and any serious study of anatomy and embryology would include drawings by Frank Netter and his colleagues.

21. O’Rahilly, R., Muller, F. (2001). Human Embryology & Teratology (3 ed). New York: Wiley-Liss.
Drs. O’Rahilly and Muller are considered to be two of the premier embryologists in the world. This is an expensive reference text. They use some of the new embryological nomenclature for human embryos. For example, the yolk sac is now called the umbilical vesicle and human embryos do not form a gastrula. All comparative embryological terms coming from other species are being totally eliminated from describing human embryos. It is expected that in 2010 a book with all the new nomenclature will be published. It will be called Embryologia Terminologia.

22. O’Rahilly, R., Muller, F. (2006). The Embryonic Human Brain: An Atlas of Developmental Stages (3 ed). New York: Wiley-Liss.
This is the first book that describes one system of the body (the brain) and takes the reader through every stage of development. The only other system of the body that is being mapped out this way is the heart and vascular system as mentioned above with Margaret Kirby’s work. It is possible to understand the lack of maturity in understanding the human embryo when only two of the nine systems of the body have been explored this thoroughly. It is an expensive reference text atlas. 26

23. Rabineau, D., Dupont, J.M., Plateaux, P. (2003). Embryologie Humaine Volume 1. CD format. Université Paris 5 – SFRS. Available from www.cerimes.education.fr.
This is perhaps the best CD of embryological images and animated movies that I have ever seen. It is all in French and to order it from the website, one must know a little bit of French to navigate the e-cart for ordering. It also requires internet access when you are playing it in order to have full access to the images and movies. This is a very worthwhile investment.

24. Rohen, J. (2007). Functional Morphology: The Dynamic Wholeness of the Human Organism. Hillsdale, NY: Adonis Press.
Dr. Rohen is an internationally renowned embryologist and anatomist in Europe. This particular book translated from the German includes the point of view of Rudolf Steiner. The book is a tour de force of the connections between morphology, embryology and adult anatomy and physiology with a little spirituality thrown in. The Steiner point of view is about the wholeness and interconnectedness of the human organism as a functional unity of mind, body and spirit. There is much more science in this book than there is spirituality.

25. Schoenwolf, G., et. al. (2009). Larsen’s Human Embryology, Fourth Edition. Philadelphia, PA: Churchill-Livingstone Elsevier.
This is a standard and excellent college text. It is used in the osteopathic and craniosacral therapy community because of its clarity and illustrations. This completely revised fourth edition is a joy to behold. The illustrations have always been excellent and new sections on fetal development and the fetus as a patient make for interesting reading. As with many new textbooks, the formatting is very user friendly. Each chapter is color-coded, which you can actually see on the edge of the pages of the book. I no longer have to put post-it notes on my favorite pages! In addition, this book gives internet access to additional illustrations, embryo animations and student consultation.

26. Steding, G. (2009). The Anatomy of the Human Embryo: A Scanning Electron-Microscopic Atlas. Basel, Switzerland: S. Karger AG.
This is a brand new atlas of human embryology. It comes from the same university in Germany where Dr. Blechschmidt taught. All the images are in black and white and very well done. It is an expensive reference atlas.

27. Sweeney, L. J. (1998). Basic Concepts in Embryology: A Student’s Survival Guide. New York: McGraw Hill.
I like this book a lot. Lauren Sweeney has done an excellent job depicting the human embryo in black and white images. It is a small paperback and an excellent companion to the Drews’ book mentioned above. It is especially oriented around the development of the face and cranium with simple drawings.

28. Tuchman-Duplessis, H., David, G., et al. (1972). Illustrated Human Embryology (Vol 1): Embryogenesis. New York: Springer Verlag.

29. Tuchman-Duplessis, H., Haegel, P. (1972). Illustrated Human Embryology (Vol 2): Organogenesis. New York: Springer Verlag.

30. Tuchman-Duplessis, H., Auroux, M., et al. (1975). Illustrated Human Embryology (Vol 3): Nervous System and Endocrine Glands. New York: Springer Verlag.
These three books are translations from the French authors. They have some of the best color drawings and illustrations I have ever seen of human embryology. I have many French anatomy books because the French seem to be able to make illustrations of the human body so simple, clear and informative. A picture is worth a thousand words. They are available in either hardback or paperback editions second hand from Amazon.

31. van der Bie, G.(2001). Embryology: Early Development from a Phenomenological Point of View. Driebergen, Nederlands: Louis Bolk Institute.
This is a small paperback and an excellent read. It is my recommended text for entry level students at any stage of academic learning. It is available as a free download from the Louis Bolk Institute in the Netherlands. The website is listed below. 28

32. Verhulst, J. (2003). Developmental Dynamics in Humans and Other Primates: Discovering Evolutionary Principles through Comparative Morphology. Ghent, NY: Adonis Press.
This is an excellent discussion of human embryology in relationship to other primates. It proposes a theory that human embryos never stop being embryos. All other species complete their embryological period by specializing in a particular body shape that allows for greater survival. For example, claws, specialized teeth for tearing, ripping and eating, specialized noses, eyes and ears, etc. The human embryo does not specialize in a particular survival oriented form. Thus the human embryo expresses the greatest degree of freedom among species on the earth. It has been said as a result that humans are perpetual embryos.

33. Vögler, H. (1987). Human Blastogenesis: Formation of the Extraembryonic Cavities. New York: Karger.
This is a small hardback book and one of my personal favorites. It focuses on the second week of embryological development. It discusses various theories of cellular differentiation and along with its excellent illustrations is the most lucid commentary I have seen on the phase of development called implantation.

34. Weihs, T. J. (1986). Embryogenesis in Myth and Science. Edinburgh: Floris Books.
I like this book because it has color images of medieval Italian frescoes. They are beautiful. It compares these images to the stages of embryological development and develops a theory that embryonic forms are a part of the human psyche. This book is one of the first to discuss human embryology with an origin mythology outside of the fields of cultural anthropology and depth psychology.

35. Wolpert, L. (1991). The Triumph of the Embryo. Oxford: Oxford University Press.
This is the first book of its kind that discusses embryonic growth and molecular genetics. It is a small hardback book.

36. http://www.embryology.ch/indexde.html
This website is new and has the best online embryology course I have ever seen. It is from Switzerland and combines the embryology departments of the Universities of Fribourg, Lausanne and Bern. It is in four languages including English and is extremely clear and precise with wonderful illustrations. It stands alone from all the other websites listed below. Additional Websites: There are many embryology websites on the internet. There is a lot of free material that can be downloaded. There are sites with animations, PowerPoint presentations and lots of written text. These are some of the sites I have explored over the past five years. It is also possible to go to Google Images and search for embryological images that way.

1. http://isc.temple.edu/marino/embryo/defaulthold.htm

2. http://www.indiana.edu/~anat550/cvanim/

3. http://www.uic.edu/com/surgery/embryo/links.htm

4. http://embryo.soad.umich.edu/index.html

5. http://cna.uc.edu/embryology/

6. http://embryology.med.unsw.edu.au/

7. http://virtualhumanembryo.lsuhsc.edu/

8. http://www.visembryo.com/baby/hp.html

9. http://home.uni-one.nl/walembryo/

10. http://www.med.upenn.edu/meded/public/berp/

11. http://nobelprize.org/medicine/laureates/1935/spemann-lecture.html

12. http://www.louisbolk.nl/index.php?Ident=comp