TRANSPORTATION OF SPERM OUTSIDE GENITAL TRACT OF MALE 189 



2. Transportation of Sperm in Forms Where Fertilization 

 OF the Egg is Internal 



a. General Features Relative to Internal Fertilization 



1) Comparative Numbers of Vertebrates Practicing Internal Fertilization. 



Of the 60,000 or more species of vertebrates which have been described, a 

 majority practice some form of internal fertihzation of the egg. Internal fer- 

 tilization, therefore, is a conspicuous characteristic of the reproductive phe- 

 nomena of the vertebrate animal group. 



2) Sites or Areas where Fertilization is Effected. The fertilization areas 

 (fig. 98) for those vertebrates which utilize internal fertilization are: 



( 1 ) the lower portions of the oviduct near or at the external orifice, 



(2) the oviduct, especially its upper extremity, 



(3) possibly the peritoneal cavity, 



(4) the follicles of the ovary, and 



(5) the brood pouch of the male (figs. 98, 106). 



Though the exact place where internal fertilization occurs may vary consid- 

 erably throughout the vertebrate group as a whole, the specific site for each 

 species is fairly constant. 



3) Means of Sperm Transfer from the Male Genital Tract to That of the 

 Female. In those fishes adapted to internal fertilization, sperm transport from 

 the male to the female is brought about by the use of the anal or pelvic fins 

 which are modified into intromittent organs (fig. 104). In the amphibia two 

 genera of Anura are known to impregnate the eggs within the oviduct of 

 the female. In the primitive frog, Ascaphus truei, the male possesses a cloacal 

 appendage or "tail," used to transport the sperm from the male to the female, 

 and the oviducts become supplied with sperm which come to lie between the 

 mucous folds (Noble, '31). (See fig. 107.) In East Africa, in the viviparous 

 toad, Nectophrynoides vivipara, fertilization is internal, and the young, a hun- 

 dred or more, develop in each uterus. (See Noble, '31, p. 74.) Just how the 

 sperm are transmitted to the oviduct and whether fertilization is in the lower 

 or upper parts of the oviduct in this species is not known. 



In contrast to the conditions found in most Anura, the majority of urodele 

 amphibia employ internal fertilization. In many species the male deposits a 

 spermatophore or sperm mass (fig. 10). The jelly-Hke substance of the sper- 

 matophore of the salamanders is produced by certain cloacal or auxiliary 

 reproductive glands. The spermatophore may in some species be picked up 

 by the cloaca of the female or in other species it appears to be transmitted 

 directly to the cloaca of the female from the cloaca of the male. As the sper- 

 matophore is held between the lips of the cloaca of the female, it disintegrates 

 and the sperm migrate to and are retained within special dorsal diverticula of 

 the cloacal wall known as the spermatheca (Noble and Weber, '29) (fig. 108). 



