1110 REPRODUCTION. [BOOK iv. 



ical problems connected with the series of changes through 

 which the ovum becomes the adult being ; or into the obscure 

 biological inquiry as to how the simple, all but structureless 

 ovum contains within itself, in potentiality, all its future devel- 

 opments, and as to what is the essential nature of the male 

 action. These problems and questions, which are fully dis- 

 cussed in other works, do not properly enter into a work on 

 physiology, except under the view that all biological problems 

 are, when pushed far enough, physiological problems. We 

 shall limit ourselves to a brief survey of the more important 

 physiological phenomena attendant on the impregnation of the 

 ovum, and on the nutrition and birth of the embryo, incident- 

 ally calling attention to some of the leading structural features 

 of the parts concerned. 



