22 6 THE HUMAN SPECIES 



The secretion of certain accessory generative glands has 

 also to be considered. The prostate secretes a thin, milky 

 fluid, consisting of so-called prostatic granules in an albumin- 

 ous liquid ; the flow is not continuous but momentary depend- 

 ing on nerve-stimuli. According to Walker, the spermatozoa of 

 man and animals only become motile when mixed with pro- 

 static secretion. 1 



Formerly the seminal vesicles were looked upon as mere 

 reservoirs for the semen ; but later observations have demon- 

 strated that they are true secreting glands producing an 

 alkaline, thin, jelly secreted continuously, which during the 

 act of coitus is ejected in conjunction with the semen. 



The physiological property ascribed to this secretion con- 

 sists in stimulating the vitality 

 and motility of the spermatozoa 

 flagellse. 



Researches on rats have proved 

 that the extirpation of these glands 

 does not interfere with the power 

 of copulation but impairs fecun- 

 dity, especially if the prostate also 

 is removed. 



The ampulla of the seminal 



FIG. 115. Fertilisation ot a mam- ducts has, according to Dissel- 



malian ovum by the sperma- horst, a great bearing upon the 



tozoa. (Haeckel.) 



duration of coitus ; when the am- 

 pulla is absent (as in canidia, pigs, felidse, viveridae, hyaenas) 

 the act is greatly prolonged. Like the majority of other 

 mammals man possesses an ampulla, and the act is soon com- 

 pleted. 



The secretion of Cowper's glands has not been isolated in 

 man. When, as in Monotremes, Cowper's are the only accessory 

 glands present, they must combine the functions of the absent 

 glands. 



Reproduction of the species can only take place in man, as 

 in all other metazoa, in one way ; for the development of one 

 single new existence the fertilisation of a female ovum by the 



o 



male semen is indispensable (Fig. 115). 



^isselhorst in A. Oppel, loc. cit., Bd. iv., p. 402. 



