II. Croonian lecture. - the developmental history of the primates

Although the embryologist has long ago given up the hope of being able to solve the phylogeny of any group of animals by his own labours alone, it is nevertheless just as true to-day as it was in the times he was buoyed up by that hope, that the data of Embryology, properly interpreted can and do furnish striking and demonstrative evidences of genetic relationships. That thesis constitutes the main theme of my discourse, and in the course of it I hope to show you how, starting from the relatively simple and generalised developmental conditions met with in the Lemuroidea, the much more specialized and secondarily modified relations found in the higher Primates may be supposed to have arisen as the result of continued adaptive modification, involving more especially acceleration and abbreviation in the developmental processes. The germ of the higher mammal, developing as it does in the uterus of the mother, has its old ancestral tendencies modified as the result of adaptation to its maternal environment and before it can proceed in earnest to carry out its primary function of forming an embryo, its most pressing necessity, since it has little or no food-reserves stored up in itself, is to make the earliest possible provision for its own nutrition. Consequently we find in the different Orders of Mammals the most varied structural adaptations designed to this end and affecting particularly the foetal membranes and their relations to the uterus. But no Order, I venture to think, can compare with the Primates in the wealth of material it provides for the study of such developmental adaptations.