449 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
No portion of the kidney in Amurus 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' 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. catws 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 app: arently 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 dorsal the impair median vein to 
the right posterior cardinal. The histological structure of the gland 
1 Loe. ctt. 
