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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. ‘l'hey 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 kidney 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 (/oc. czt.), that im Gadoids and Pleuro- 
