738 GENERATION AND DEVELOPMENT. 



that of the testicles, and serve as reservoirs for the seminal 

 fluid. The former is their most constant and probably 

 most important office ; for in the horse, bear, guinea-pig, 

 and several other animals, in whom the vesiculse seminales 

 are large and of apparently active function, they do not 

 communicate with the vasa deferentia, but pour their 

 secretions, separately, though it may be simultaneously, 

 into the urethra. In man, also, when one testicle is lost, 

 the corresponding vesicula seminalis suffers no atrophy, 

 though its function as a reservoir is abrogated. But how 

 the vesiculae seminales act as secreting organs is unknown ; 

 the peculiar brownish fluid which they contain after death 

 does not properly represent their secretion, for it is different 

 in appearance from anything discharged during life, and 

 is mixed with semen. It is nearly certain, however, that 

 their secretion contributes to the proper composition of the 

 impregnating fluid ; for in all the animals in whom they 

 exist, and in whom the generative functions are exercised 

 at only one season of the year, the vesiculae seminales, 

 whether they communicate with the vasa deferentia or not, 

 enlarge commensurately with the testicles at the approach 

 of that season. 



That the vesiculee are also reservoirs in which the semi- 

 nal fluid may lie for a time previous to its discharge, is 

 shown by their commonly containing the seminal filaments 

 in larger abundance than any portion of the seminal ducts 

 themselves do. The fluid-like mucus, also, which is often 

 discharged from the vesiculee in straining during defeca- 

 tion, commonly contains seminal filaments. But no reason 

 can be given why this office of the vesiculso should not be 

 equally necessary to all the animals whose testicles are 

 organized like those of man, or why in many animals the 

 Vesiculse are wholly absent. 



There is an equally complete want of information re- 

 specting the secretions of the prostate and Cowper's 

 glands, their nature and purposes. That they contribute to 



