292 CLASS AMPHIBIA. 



which is not found in fishes and into which the urinary ducts 

 do not open as they do in mammals. There is no copulatory 

 organ (though in the Gymno'phiona the cloaca can be extruded 

 and used as such). There is a lobed fat-body frequently connected 

 to the front end of the generative gland. There is always a 

 functional pronephros in the larva Avhich atrophies in the adult. 

 In the salamander or newt, which may be taken as type, the 

 kidney is much narrower in front than it is behind (Fig. 163). 

 The narrower, anterior portion may be called the sexual part, 

 because in the male the testis is coimected with it by the testi- 

 cular network. It is also sometimes called the mesonephros 

 because it corresponds roughly to the mesonephros (Wolffian 

 body) of the embryos of the Sauropsida and Mavimalia. In 

 this case the posterior thicker portion might be called the 

 metanephros, on the view that it corresponds to the permanent 

 kidney of the higher types. The duct runs by the side of the 

 sland and receives the collecting tubes. In the male the col- 

 lecting tubes of the metanephros are inclined backwards and all 

 join to open at one point into the longitudinal duct close to the 

 cloaca (Fig. 163 a). An incipient ureter is thus formed. In 

 this case the longitudinal duct is mainly associated with the 

 anterior sexual part of the kidney or mesonephros and is for that 

 reason frequently spoken of as the mesonephric duct (Leydig's 

 duct). 



The renal tubules (nephridia) consist of four parts, (1) tlie collecting 

 tubule, which is continuous in the kidney with (2) the contorted tubule 

 which is the especially glandular part, and passes into (3) the malpighian 

 body, from which passes (4) the peritoneal canal to the body-cavity 

 opening (nephrostome) placed on the ventral surface of the kidney (Fig. 

 1C4). The contorted tubule and peritoneal canal usually join before 

 opening into the malpighian body (Fig. 164 mk'). Such a tubule is called 

 a primary or simple tubule. The anterior part of the kidney (mesonephros) 

 of Urodeles consists entirely of such primary tubules. In the metanephros 

 however we find compovind tubules. These consist of primary tubules 

 each with its nephrostome, and of a number of dorsally placed secondary 

 tubules (also with nephrostomes) which open into the collecting part of 

 the primary tubule. The primary tubules are not arranged segmentally 

 in any Amphibian, except the Gymnophiona. The number of primary 

 tubules in a segment is greater in the posterior than in the anterior part 

 of the kidney. The testicvilar network or cormection between the testis 

 and mesonephros is constructed as follows (Fig. 163). There is a longi- 

 tudinal duct, called the longitudinal duct of the testis (not shown in fig.), 

 running along the base of the testis and receiving the testicular tubules. 

 This gives off an irregular number of canals — the vasa efferentia — which 



