*- I 



CHAPTER XIII. 

 REPRODUCTION. 



VERY many facts in our knowledge of reproduction de- 

 pend on observations made upon lower animals, but there is 

 sufficient analogy between the known facts connected with 

 human reproduction and development and those of the same 

 stages in other groups of beings to enable us to present, as at 

 least approximately accurate, certain broad principles regard- 

 ing the process as it pertains to the human race. 



In order that a human being may be brought into exist- 

 ence it is necessary that there be a union of the male ele- 

 ment, the spermatozoon, and the female element, the ovum. 

 Both these sexual cells are developed from epithelium the 

 spermatozoon from that of the seminiferous tubules of the 

 male, and ovum from the germinal layer of the ovary. 



In what follows reference will be had to reproductive pro- 

 cesses in the human being. 



Spermatozoa. Human spermatozoa (Fig. 92) are elon- 

 gated bodies, about one five-hundredth of an inch in length, 

 and consist of three parts, head, mid-portion and tail. The 

 last-named part is about four-fifths the length of the entire 

 spermatozoon. The head is egg-shaped and much the thick- 

 est part of the element. A slender filament, the axial fiber, 

 extends throughout its length from head to tail and projects 

 slightly beyond the latter. Spermatozoa are possessed of 

 wonderful vitality. They live for several weeks in the geni- 

 tal passages of the female. In the male genital passages they 

 may live for months in a quiescent state. The nucleus is the 

 fertilizing agent. Spermatozoa are also remarkable for 

 their power of locomotion, which is effected by lashing? 

 and rotary movements of the tail. 



328 



