1366 PHYSIOLOGY 



mixed with prostatic secretion. It is difficult to understand how the 

 spermatozoa are conveyed through the resistance which must be 

 offered by the huge length of the tubule of the epididymis, unless their 

 onward motion is facilitated by the cilia-like structures attached to 

 some of the cells lining this tubule. The formation of the spermatozoa 

 is continuous, though the rate at which this occurs is variable and 

 regulated by the sexual activity of the individual. In the fully formed 

 semen the spermatozoa formed by the testis are mixed not only with 

 the fluid secreted by the lining membrane of the epididymis and of the 

 seminal vesicle but also with the mucous secretions of the prostatic 

 glands and of Cowper's glands. Nevertheless it contains spermatozoa 

 in enormous numbers, the semen emitted at a single act of coitus 

 containing as many as 226,000,000 spermatozoa. Though the vast 

 majority of these are probably capable of fertilising an ovum, this act is 

 carried out by only one- a fact characteristic of the prodigality of 

 nature when dealing with the perpetuation of the type. 



THE FEMALE REPRODUCTIVE ORGANS 



The essential organ of reproduction in the female is the ovary, the 

 seat of production of the ova. The accessory organs include the ovi- 

 ducts or Fallopian tubes, the uterus, in which the fertilised ovum is 

 retained during the first nine months of its development, and the 

 vagina, which is especially adapted for the reception of the male organ 

 in the act of impregnation. 



Among the accessory organs we may also reckon the mammary 

 glands, which undergo a special development during pregnancy, and 

 serve for the nourishment of the young individual during the first 

 period of extra-uterine life. 



OVULATION. At birth the ovary consists of a stroma of spindle- 

 shaped cells, and is covered by a layer of cubical epithelium (the germ- 

 epithelium) continuous with the endothelium lining the general peri- 

 toneal cavity. Embedded in the stroma, but especially numerous just 

 underneath the epithelium, are a vast number of * primordial follicles.' 

 These are formed during foetal life by down-growths of the germinal 

 epithelium . Of the cells prolonged in this way from the germinal epithe- 

 lium, some undergo enlargement to form the primordial ova, while the 

 others are arranged as a single layer of flattened nucleated cells, the 

 ' follicular epithelium,' as a sort of capsule to the ovum. Of the pri- 

 mordial follicles, about 70,000 are to be found in the ovary of the 

 new-born child. During the first twelve to fourteen years of life 

 they remain in a quiescent condition. With the onset of puberty 

 one or more of the primordial follicles begin to develop. Indeed, 

 this development may be regarded as the causative factor in the 

 various phenomena which are characteristic of puberty in the female 



