CHAPTER XXVI 



REPRODUCTION AND GROWTH 



FIRST SECTION 



REPRODUCTION 



THE physiology of reproduction in general covers so wide a field and is 

 related to so many branches of biology that even a superficial presentation 

 of its most salient features would require more space than we have at our 

 disposal. We shall therefore limit the discussion to those features of repro- 

 duction in man and the higher animals which are very important from the 

 standpoint of human physiology, but which are not usually treated as belong- 

 ing to the special province of embryology. The following brief survey of 

 this field will indicate the scope we have in mind. 



Reproduction in most of the higher animals is inaugurated by the conjuga- 

 tion of two different sexual, elements, the male and the female. The female 

 element, the ovum, is formed in the ovary: it was first demonstrated for the 

 mammals by v. Baer in 1827. The male element, the spermatozoon, is formed 

 in the testes and represents the " seminal bodies " discovered by Leuwenhoeck 

 in 1677. 



In mammals the spermatozoa are introduced into the female body by the 

 act of copulation. If fertilization of the ovum then takes place, there develops 

 within the female body a new individual, which, when it has reached a certain 

 stage in its development, is expelled from the body of the mother. This 

 latter process is called birth or parturition. 



At birth the new individual is not developed far enough to seek inde- 

 pendently and to utilize the ordinary food of the species, but must for a time 

 derive its nourishment from the mother. The milk glands of the mother 

 at this time are roused to a high degree of activity, and furnish a secretion, 

 the milk, which contains in proper proportions the foodstuffs necessary for 

 the maintenance of the newborn child. 



The physiology of reproduction, as we shall limit the subject here, will 

 accordingly include : the functions of the male and female sexual organs, the 

 processes of copulation and conception, birth, and the secretion of milk. 



1. THE MALE SEXUAL ORGANS 



These are: the testes, which produce the spermatozoa; the accessory glands 

 (vesicular glands, prostate body, and the glands of Cowper), which produce 



