The early development of the mammalian embryo belongs to a period which, for the student, provides the particularly deep fascination connected with the processes of germination of the fIrst tender buds of life. Moreover, developmental biology encompasses a very large part of biology; if broadly dermed - almost all of it. The same is true for the fIeld of pathology if the manifold possibilities of disorders of the orderly arranged pathways of developmental processes are considered. Normal development in its earliest steps - and it would be diffI- cult to see it otherwise - means the functioning of very intricate systems of complex inter- dependent cycles controlled by structural, genetic, physiological and biochemical determi- nants. However, disturbances interfering with them in their very different ways, can lead to fetal death, disorders of growth and differentiation, malformation and disease, sometimes as late as in the next generation or later. This is, indeed, the concern of the pathologist to whom and to whose interest in developmental pathology, this book is dedicated. The outlines of the present volume were conceived at a symposium on "Control of early em- bryogenesis and factors responsible for failure of embryonic development" held May 1-4, 1974 in Travemtinde and sponsored by the Deutsche Forschungsgemeinschaft. Almost fIfty active participants attended this conference. At the time and in keeping with the purpose of the conference, publication of the proceedings was not envisaged.