364 



COMPARATIVE MORPHOLOGY OF VI . 



\TES 



and urodeles, but in the adult anura the nephrostomes separate from the 

 nephridial tubules and join branches of the renal blood-vessels, thus placing the 

 coelom in connexion with the circulatory system. 



In the urodeles (fig. 384) the mesonephroi form a pair of ridges or project- 

 ing folds on the dorsal wall of the coelom. Their length is somewhat propor- 

 tional to the body length, and the anterior end of each loses its excretory 

 character, and in the male becomes subservient to reproduction, as described 

 above (p. 351). The caecilians (fig. 385) resemble the urodeles except that the 



mesonephroi are more lobulated, the result of 

 aggregates of secondary tubules around the 

 collecting tubules. In the anura the organs are 

 more compact and the differentiated anterior 

 end is lacking, although the efferent ductules of 

 the testes pass through the mesonephros. The 

 nephridial waste, in aU cases, is carried away 

 by the Wolffian duct, while, in the males, the 

 same duct acts as a vas deferens as in the 

 elasmobranchs. The ducts of the two sides open 

 separately into the cloaca, and in the males 

 each usually has an enlargement, the seminal 

 vesicle, which in the breeding season, is a res- 

 ervoir for the spermatozoa. The urinary 

 bladder differs from that of the ichthyopsida in 

 being ventral to the cloaca. It is of the 

 allantoic type. It is very long in the caecilians 

 and in Amphmma, saccular in most urodeles, 

 and bifid at the tip in the majority of anura, 

 being even divided into two sacs, connected 

 only at the opening into the cloaca in some 

 species. 



Fig. 386. — Urogenital organs The sexual organs of the amphibia fit well 

 of male frog ventral view. The j^^o ^^^ ^^^^^]^ scheme. The gonads . are 

 left testis (0 has been turned to , , . , 1 7 ex. 



the right to show the efferent roughly correlated m form to the shape of the 

 ductules (e). i, urinary bladder; body, being compact in the anura, longer in 

 a, adrenal organ;/, fat body (that ., ..-.oHpIp^ anH Inntrpst in thp rjprilians 

 of the left side removed); /, longi- ^^^ urodeles, and longest m tne cajcilians. 



tudinal duct; m, mesonephros; p. The testes have both the longitudinal and 



postcava; r, rectum; s, seminal the testicular canals connecting the efferent 



receptacle; w, WolflSan duct. j ^ i .1 1 ^. • ^v, i, *u 



^ ' ductules, these latter passmg through the 



anterior part of the mesonephros, sometimes utilizing the nephridial tubules, 

 sometimes pursuing their own course, the two conditions being found in dif- 

 ferent species of frog (Rana) in Europe. The relations in the American species 

 are not known. In the caecilians (fig. 385) the testes resemble two strings of 

 beads, each bead consisting of a number of seminiferous tubules, the string of 

 either side being connected by the testicular canal. In urodeles the testes are 

 shorter and in the anura they are oval or rounded. 



The ovaries are saccular, with an internal cavity lined with pavement epi- 

 thelium. The eggs do not escape into this as in the teleosts, but into the body 



