MALE ORGANS OF GENERATION. 561 



while the spermatozoa remaining entangled in the filter, if mixed 

 with a sufficient quantity of fluid of the requisite density for dilu- 

 tion, may still be successfully used for the impregnation of eggs. 

 It is well known, also, that animals or men from whom both testi- 

 cles have been removed, are incapable of impregnating the female 

 or her eggs ; while a removal or imperfection of any of the other 

 generative organs does not necessarily prevent the accomplishment 

 of the function. 



In most of the lower orders of animals there is a periodical 

 development of the testicles in the male, corresponding in time with 

 that of the ovaries in the female. As the ovaries enlarge and the 

 eggs ripen in the one sex, so in the other the testicles increase in 

 size, as the season of reproduction approaches, and become turgid 

 with spermatozoa. The accessory organs of generation, at the 

 same time, share the unusual activity of the testicles, and become 

 increased in vascularity and ready to perform their part in the 

 reproductive function. 



In the fish, for example, where the testicles occupy the same 

 position in the abdomen as the ovaries in the opposite sex, these 

 bodies enlarge, become distended with their contents, and project 

 into the peritoneal cavity. Each of the two sexes is then at the 

 same time under the influence of a corresponding excitement. The 

 unusual development of the generative organs reacts upon the entire 

 system, and produces a state of peculiar activity and excitability, 

 known as the condition of " erethism." The female, distended with 

 eggs, feels the impulse which leads to their expulsion ; while the 

 male, bearing the weight of the enlarged testicles and the accumu- 

 lation of newly-developed spermatozoa, is impelled by a similar 

 sensation to the discharge of the spermatic fluid. The two sexes, 

 accordingly, are led by instinct at this season to frequent the same 

 situations. The female deposits her eggs in- some spot favorable 

 to the protection and development of the young ; after which the 

 male, apparently attracted and" stimulated by the sight of the new- 

 laid eggs, discharges the spermatic fluid upon them, and their 

 impregnation is accomplished. 



In such instances as the above, where the male and female gene- 

 rative products are discharged separately by the two sexes, the 

 subsequent contact of the eggs with the spermatic fluid would seem 

 to be altogether dependent on the occurrence of fortuitous circum- 

 stances, and their impregnation, therefore, often liable to fail. In 

 point of fact, however, the simultaneous functional excitement of 

 36 



