Rudiments of the testicular network are found in the female Cœciliidæ and in the females of many Urodela (Salamandra, Triton). These rudiments may in their fullest development consist of a longitudinal canal and of transverse canals passing from this to the Malpighian bodies, together with some branches passing into the mesovarium.
Amongst the Urodela the collecting tubes of the hinder non-sexual part of the Wolffian body, which probably represents a rudimentary metanephros, undergo in the male sex a change similar to that which they usually undergo in Elasmobranchii. Their points of junction with the Wolffian duct are carried back to the hindermost end of the duct ([fig. 400] B), and the collecting tubes themselves unite together into one or more short ducts (ureters) before joining the Wolffian duct.
In Batrachoseps only the first collecting tube becomes split off in this way; and it forms a single elongated ureter which receives all the collecting tubes of the posterior segmental tubes. In the female and in the male of Proteus, Menobranchus, and Siren the collecting tubes retain their primitive transverse course and open laterally into the Wolffian duct. In rare cases (Ellipsoglossus, Spengel) the ureters open directly into the cloaca.
The urinary bladder of the Amphibia is an outgrowth of the ventral wall of the cloacal section of the alimentary tract, and is homologous with the allantois of the amniotic Vertebrata.
The subjoined diagram ([fig. 400]) of the urogenital system of Triton illustrates the more important points of the preceding description.
In the female (A) the following parts are present:
(1) The Müllerian duct or oviduct (od) derived from the splitting of the segmental duct.
(2) The Wolffian duct (sug) constituting the portion of the segmental duct left after the formation of the Müllerian duct.
(3) The mesonephros (r), divided into an anterior sexual part connected with a rudimentary testicular network, and a posterior part. The collecting tubes from both parts fall transversely into the Wolffian duct.
(4) The ovary (ov).
(5) The rudimentary testicular network.
In the male (B) the following parts are present:
(1) The functionless though fairly developed Müllerian duct (m).
(2) The Wolffian duct (sug).
(3) The mesonephros (r) divided into a true sexual part, through the segmental tubes of which the semen passes, and a non-sexual part. The collecting tubes of the latter do not enter the Wolffian duct directly, but bend obliquely backwards and only fall into it close to its cloacal aperture, after uniting to form one or two primary tubes (ureters).
(4) The testicular network (ve) consisting of (1) transverse ducts from the testes, falling into (2) the longitudinal canal of the Wolffian body, from which (3) transverse canals are again given off to the Malpighian bodies.
Fig. 400. Diagram of the urinogenital system of Triton. (From Gegenbaur; after Spengel.)
A. Female. B. Male.
r. mesonephros, on the surface of which numerous peritoneal funnels are visible; sug. mesonephric or Wolffian duct; od. oviduct (Müllerian duct); m. Müllerian duct of male; ve. vasa efferentia of testis; t. testis; ov. ovary; up. urinogenital pore.