224 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



tubules, which are somewhat sparsely distributed in the 

 anterior part of the organ, but are very abundant in the 

 thickened posterior portion. They are greatly convoluted 

 tubules of varying diameter opening into the ureters. It 

 is somewhat remarkable that Malpighian bodies are very 

 difficult to find, and indeed seem to be absent, in some 

 parts at least, of the kidney. This condition is connected 

 with the vascular arrangements of the organ. By far the 

 greater portion of the blood entering it is venous, and the 

 arterial supply is very scanty. Two, or at most three, very 

 small vessels originating directly in the dorsal aorta enter 

 at the dorsal surface, and the common genital artery 

 (A. gen., fig. 22) gives off several very fine arterial twigs 

 which ramify in the posterior portion. The whole arterial 

 blood supply is very small compared with the amount of 

 venous blood entering by the renal portal veins. 



The lymphoid tissue which is so frequently met with 

 in the kidneys of fishes is most abundant in the middle 

 and anterior regions of the plaice kidney. It consists of 

 very small cells, supported by reticular connective tissue, 

 and filling up the interspaces between the blood vessels 

 and the uriniferous tubules. Groups of pigment granules 

 are scattered throughout this lymphoid tissue and give the 

 organ its black appearance. They are small rounded 

 granules of variable diameter, and of a greenish-black 

 colour. They lie freely among the lymphoid cells. 



The Pronephros and Head Kidney (Text-fig. 2). — 

 The kidnejr in Pleuronectes is a mesonephros, and its 

 paired ducts are segmental or archinephric ducts. The 

 most common mode of origin of these structures in 

 Teleosts is by a longitudinal evagination of somatopleure 

 forming a groove which afterwards closes by constriction 

 of its lips, giving rise to a tube. Mcintosh and Prince 

 state, however (loc. cit.), that in Gadoids and Pleuro- 



