EXCRETORY ORGANS OF VERTEBRATA. 



605 



which, however, several ureters may open separately. In the 

 females, also, the efferent ducts from the anterior and aborted 

 portion of the primitive kidney are connected with the ureter. 



In the Ganoi'dei and Teleostei the kidneys have the same posi- 

 tion. The primitive kidney appears to be considerably increased in 

 size, while the efferent ducts are not so completely differentiated as 

 in the Selachii, where they were the cause of much complication ; in 

 the Ganoi'dei, however, the presence of a nephrostome, with a wide 

 abdominal orifice on the efferent duct, speaks to the commencement 

 of the process by which the Mullerian duct 

 is differentiated; the ureter, therefore, no 

 longer corresponds to the archinephric duct. 



In the Teleostei the secondary portion 

 of the gland first appears on the anterior 

 division of the archinephric duct, and 

 forms that portion which, in many, extends 

 as far as the head (head-kidney). The 

 hinder portion, which is developed later, 

 becomes connected with this. The whole 

 forms a compact glandular organ, which is 

 covered by the peritoneum, and extends 

 along the vertebral column; it varies in 

 size in different regions. Its differentiation 

 into lobes is generally implied by the 

 greater development of certain regions. 

 The efferent ducts (Fig. 345, u) either pass 

 along the anterior surface, or more to the 

 sides ; they generally unite into an unpaired 

 portion, which opens behind, or below the 

 generative orifice. The ducts are widened 

 at different points, either in the common, 

 or in the separate portions ; these struc- 

 tures function as " urinary bladders," but 

 they have no morphological connection 

 with the urinary bladder of the higher 

 Vertebrata. 



The renal organs of the Amphibia have 

 many points in common with those of the 



Selachii. The rudimentary ducts are always provided with func- 

 tionally active nephrostomata. The primary ureters form lobules 

 by becoming arranged in coils. In the Coecilia) they are all of 

 much the same size, but in the Urodela and Anura the hinder ones 

 are increased in size and number, so that this portion becomes 

 much larger than the anterior part. The nephrostomata, also, are 

 greatly increased in number in this region, and are persistent. 

 In the Urodela the anterior portion of the kidneys receives the 

 efferent ducts of the testes, while in the Ccecilia3 and Anura 

 different parts of the kidneys are connected with these organs. 

 The primary archinephric duct is differentiated so as to give rise 



Fig. 3-15. Kidneys of Salmo 

 fario. R Kidneys, u Ureter. 

 v Vesicular enlargement. 

 ur Its efferent duct, rr Venaa 

 renalesrevehentes. d Ductus 

 Cuvieri. s Vena subclavia 

 (after Hyrtl). 



