442 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



No portion of the kidney in Amiurus lies above the air-bladder. 

 The only connection between the head-kidney and the posterior part 

 is the cardinal veins. Ignorance of the change of function in the 

 former, no doubt, led Hyrtl 1 to state that the ureters also served to 

 connect them, but the fact is that all trace of the ureters beyond the 

 posterior part has disappeared before the metamorphosis of the gland 

 itself is completed. 



The functional kidney (mesonephros) is a single gland measuring 

 in large specimens of A. catus 25 mm. across the ventral surface 

 behind the air-bladder ; 35 mm. from its apex to the surface of the 

 air-bladder; 25 mm. to the posterior point of the air-bladder in the 

 median line. A dorso- and a ventro-lateral horn fills up the space 

 between the rounded posterior end of the air-bladder and the body- 

 wall. The length along the ventro-lateral edge from the apex of the 

 gland to the point of the horn is 45 mm. 



The only indication of the paired character of the gland is to be 

 found in its ducts and blood-vessels. There is a pair of ureters 

 which by their numerous branches drain the right and left half of 

 the kidney respectively, and unite as they leave its posterior point 

 just at the urinary bladder. In most cases they appear to unite 

 sooner, even as far forward as the middle of the gland, but in all 

 specimens examined, the adjacent walls were found to persist as a 

 partition as far as the bladder. 



The urinary bladder is apparently a mere diverticulum of the 

 ventral wall of the urinary canal. As it always lies upon the right 

 side of the genital organs and rectum, it must represent the right 

 horn of the bladder, but there is no rudiment of a left horn present 

 as found by Hyrtl in Silurus glanis. Its length is about double its 

 width, but the actual size varies in different individuals. It opens 

 into the wide urethra, which is about 12 mm. in length, and opens 

 on a papilla behind the anus. 



The large vessels and ducts of the kidney, to which reference has 

 already been made, occupy the following relative positions : The 

 caudal vein passes downwards between the ureters, and then gives 

 off its branches which lie near the ventral surface. Above these are 

 the paired ureters, and still more dorsj.1 the impair median vein to 

 the right posterior cardinal. The histological structure of the gland 



