GENERATION AND DEVELOPMENT. 251 



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 com- 

 mensurately with the testicles at the approach of that season. 



That the vesiculaa are also reservoirs in which the seminal fluid may 

 lie for a time previous to its discharge, is shown by their commonly con- 

 taining 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 vesiculae in straining during defaecation, commonly 

 contains seminal filaments. But no reason can be given why this office 

 of the vesiculae should not be equally necessary to all the animals whose 

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

 vesiculae are wholly absent. 



There is an equally complete want of information respecting the secre- 

 tions of the prostate and Cowper's glands, their nature and purposes. 

 That they contribute to the right composition of the impregnating fluid, 

 is shown both by the position of the glands and by their enlarging with 

 the testicles at the approach of an animal's breeding time. But that they 

 contribute only a subordinate part is shown by the fact, that, when the 

 testicles are lost, though these other organs be perfect, all procreative 

 power ceases. 



THE SEMEN. 



The mingled secretions of all the organs just described, form the 

 semen, which is a thick whitish fluid composed of a liquor seminis and 

 spermatozoa, with detached epithelial cells. The fluid part has not 

 been satisfactorily analyzed: but Henle says it contains fibrin, because 

 shortly after being discharged, flocculi form in it by spontaneous coagu- 

 lation, and leave the rest of it thinner and more liquid, so that the fila- 

 ments move in it more actively. 



Nothing has shown what it is that makes this fluid with its corpuscles 

 capable of impregnating the ovum, or (what is yet more remarkable) of 

 giving to the developing offspring all the characters, in features, size, 

 mental disposition, and liability to disease, which belong to the father. 

 This is a fact wholly inexplicable: and is, perhaps, only exceeded in 

 strangeness by those facts which show that the seminal fluid may exert 

 such an influence, not only on the ovum which it impregnates, but, 

 through the medium of the mother, on many which are subsequently im- 

 pregnated by the seminal fluid of another male. 



