Chap. VII.] 



FISHES; AMPHIBIA. 



259 



another before they open into the common efferent 

 duct, and the pronephros would appear to be absent 

 even at the very earliest stages. In them, as in Fishes 

 generally, the renal organs are of great length, as com- 

 pared with those of the higher Yertebrata. 



In the sturgeon, among the Oanoids, the kidneys 

 extend from just behind the skull as far as the cloaca, 

 and differ in width in different regions ; in them, and 



A I B 



Fig. 106. Mesonephros of Bdellostoma. 



A. ff.,Segmental duct ; 6, segniental tube ; c, glomeruHie. B. A part more highly 

 magnified, showing one duct with its afferent vessel d, and its efferent e. 

 (After J. Mill lef.) 



in the Teleostei, there is a great reduction in the 

 number of separate ductules which pass from the sub- 

 stance of the kidney into the efferent duct. 



In the Urodela the mesonephros is of considerable 

 length, and gives off a number of ducts (Fig. 107) ; in 

 the ffogy which may be taken as a type of the Aimra, 

 the kidney is much shorter, and the efferent duct 

 (ureter) is closely applied to the lower third of the 

 kidney ; if, however, we make an examination of a 

 longitudinal section of the kidney under a low magni- 

 fying power, we shall see that the substance of that 



