The first few months of any pregnancy are of supreme importance to the success of that pregnancy. This statement is so obvious as to be almost a platitude, yet it must be said that no aspect of pregnancy has been more neglected in the human than the first three months. Little is known of the morphological changes that occur at that time and our knowledge of the mechanisms that control this vital stage of pregnancy is almost non-existent. The explanation for this neglect of what is an obvious area for study is the difficulty of obtaining normal material. It is rare to have material to study...