184 AMPHIBIA. 



The lymphatic vessels of the Amphibia accompany the blood- 

 vessels as plexuses, or as wide lymphatic sinuses. In certain places 

 the l^mph receptacles are rhythmically contractile, and have the 

 value of lymph hearts. In the Salamanders and Frogs there are two 

 lyinph hearts beneath the dorsal integument in the scapular region, 

 and two close behind the ileum. Of the vascular glands the most 

 noteworthy are the thymus, which is always paired, and the spleen, 

 which is never absent. 



The urinary organs (fig. 625) are paired kidneys, the numerous 

 collecting tubules of which enter the ducts of the primitive kidney ; 

 these open on wart-like protuberances on the dorsal wall of the cloaca. 

 The urinary bladder is an unpaired diverticulum of the ventral wall 

 of the cloaca : it is visually bifid at its free end. 



In all cases there is a close relation between the urinary organs 

 and the efferent ducts of the generative organs (fig. 625). As in 

 the higher Vertebrates the primitive kidney (Woltfian body or 

 mesonephros) in part becomes the epididymis and the efferent 

 apparatus of the testis, so also in the Amphibia a part at least of the 

 primitive kidney, which in these animals persists as a urinary organ, 

 functions as epididymis. The vasa efferentia sink into the kidneys and 

 become connected with the urinary tubules, and thus conduct their 

 contents, usually by means of a common duct, into the terminal 

 portion of the duct of the primitive kidney, which functions as a 

 urogenital duct. In the Salamanders there are, in addition, glands 

 called prostate glands on the wall of the cloaca. In the female 

 sex the Miillerian duct, which is rudimentary in the male, assumes 

 the function of oviduct. This duct begins with a free funnel-shaped 

 dilated opening into the body cavity, takes a sinuous course, and opens, 

 often after forming a uterus-like dilation, with the urinary duct 

 laterally into the cloaca, in the wall of which, in the Salamandrina 

 according to v. Siebold's discovery, saccular glands functioning as 

 seminal receptacles are placed. A complete hermaphroditism seems 

 never to occur, although in the male Toad, especially in Bufo 

 variabilis, rudiments of the ovaries have been found near the testes. 



Males and females are often distinguished by their size and colour, 

 and also by other peculiarities (vocal sacs), which are especially pro- 

 minent at the breeding season in spring and summer. In spite of 

 the absence of external organs of copulation, sexual intercourse takes 

 place, but it usually consists merely of an external approximation of 

 the two sexes (Batrachians), and has for its consequence a fertilisation 

 of the eggs outside the body of the mother. The male Salamanders 



