100 



CHAPTER XVIII. 



ORGANS OF GENERATION IN THE VERTEBRATA. 

 PISCES. 



In this extensive class, the generative apparatus is comparatively 

 simple, consisting in the female osseous family of two large mem- 

 branous ovaries, with short oviducts, opening in the vicinity of the 

 anus. The ova are generally very numerous, and are deposited in 

 shallow water where they receive the fecundating influence of the 

 male, and the genial heat of the solar rays. In the males the tes- 

 ticles are of great size and composed of a congeries of convoluted 

 tubes; the semen is discharged by the vasa deferentia, and diffused 

 through the water in the neighbourhood of the ova, which are thus 

 impregnated. The presence of a penis in this class is not necessary, 

 seeing that copulation does not occur; to this, however, there are 

 a few exceptions, in which the ova are fecundated prior to their 

 discharge; and in the blennius viviparus, the young are produced 

 alive, being hatched within the oviduct. In these rare instances, 

 the vas deferens protrudes externally in the form of a little penis. 

 In the eel, the lamprey, and many cartilaginous fishes, the ova are 

 suspended in the interior of the abdomen where they receive the 

 influence of the semen, and are discharged by a simple orifice near 

 the anus. 



AMPHIBIA. 



The ovaria of these animals are smaller, but in other respects 

 similar to those of the lamprey ; the oviducts are long and tortuous; 

 they commence by a fimbriated extremity, and previous to their 

 termination in the cloaca they enlarge to retain the ova for some 

 time before expulson. In the frog, the testicles, which are two in 

 number, are placed on the kidneys, and their excretory tubes dis- 

 charge themselves into the ureters. In the majority of instances, 

 the ova are fecundated in exitu by the sprinkling of the semen from 

 the male which is placed on the back of his mate. In the triton, 

 and a few others, the semen diffused through the water passes into 

 the genital organs and produces internal impregnation. The sala- 

 mander alone possesses a rudimentary penis, and in this case, too, 

 the eggs are hatched within the oviduct. 



The reptilia, for the greater part, possess a generative system, 

 the same as the amphibia ; the higher orders accomplish internal 

 impregnation. The males of serpents' are generally provided with 

 two penises which, instead of being perforate, are grooved for the 

 passage of the semen into the cloaca of the female. In the sauria 

 the penis is bifid, and its extremities covered with recurved spines. 



