Although a human embryo possesses so much grace that the untutored spectator can only admire it in awe, this minute and humble embryo is still almost unknown to many. For some, it seems to belong to the animal kingdom only; others see in it man in his most primordial and elementary aspect. The early life of man thus has become a problem. The development of man as individual (individual development) begins with fertilization. The following pages, therefore, concentrate above all on the develop­ ment from the ovum to the embryo. The description given below of the ontogenesis of the human embryo and its early functions has