350 REPRODUCTION. [BOOK iv. 



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 developments, and as to 

 what is the essential nature of the male action. These problems 

 and questions, which are fully discussed 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, physio- 

 logical 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, incidentally calling attention to some of the leading 

 structural features of the parts concerned. 



