222 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



from the 2nd to the 14th vertebrae. Its greater portion is 

 covered laterally by the transverse processes and ribs of 

 those vertebrae. Its ventral surface forms the roof of the 

 body cavity. Posteriorly it increases very much in thick- 

 ness dorso-ventrally and occupies the angle formed by the 

 vertebral column and the nearly perpendicular 1st haemal 

 spine and axonost, and laterally by the 7th to 10th ribs. 

 It is for the greater portion of its length a single un- 

 divided mass, but anteriorly is produced into two lapering 

 and diverging horns — the head portions of the kidney, 

 which lie laterally and dorsally from the oesophagus. The 

 right unpaired cardinal vein runs along the middle line as 

 far as the thickened portion, and is visible on its ventral 

 surface. Dorsally the aorta lies in a groove in the middle 

 line, and this with the cardinal vein separates the 

 uriniferous tubular tissue into two paired masses. Only 

 in the thickened posterior portion of the kidney is this 

 tubular tissue continuous across its whole breadth. 



At the dorsal posterior corner of the kidney the caudal 

 vein enters as a single vessel which almost immediately 

 divides into paired portions. Apparently it does not 

 become continuous with the cardinal vein, but breaks up 

 round the uriniferous tubules, though there are doubtless 

 anastomoses between the two vessels. The extreme 

 ventral portion of the kidney is produced downwards into 

 paired tips, and into these the paired genital veins {V .gen. 

 fig. 21) enter. Along the dorsal surface of the organ other 

 paired venous trunks (parietal veins) also enter. The 

 most anterior of these vessels is shewn in fig. 22 entering 

 the extreme anterior tip of the head portion of the kidney. 

 The caudal, genital and parietal veins, with the renal 

 arteries are the afferent vessels of the kidney. The paired 

 posterior cardinal veins are its efferent vessels. 



The Ureter (Uret. fig. 21) leaves the ventral and pos- 



