346 



FISHES 



two contiguous lobes of lymphoid tissue which apparently 

 represent a thymus. 



The Supra-renal Bodies. — The supra-renal bodies are organs 



of problematic function, which are present in the Cyclostomata, 



ggg and probably in all 



Fishes, and situated 

 in close proximity 

 to the kidneys. 



In the Cyclosto- 

 mata {Petromyzon) 

 these bodies are re- 

 presented by lobules 

 of cells along the 

 posterior cardinal 

 veins, and also by 

 masses of peculiar 

 cells (" chromaffin 

 cells ") along the sides 

 of the aorta and seg- 

 mental arteries.^ In 

 Elasmobranchs there 

 are two distinct 

 structures, the paired 

 supra-renals and the 

 inter -renals (Fig- 

 203, A). The former 

 are a series of pairs of 

 segmentally arranged 

 bodies, situated on 

 the successive pairs 

 of segmental arteries 

 given off from the 

 dorsal aorta. The 

 two bodies which 

 form the first pair are much larger than any of the others, and were 

 formerly spoken of as " axillary hearts." The inter-renal is usually 

 a, thin elongated " ochre-yellow " body, from which one or two lobes 

 may be detached in front, and extends for a variable distance in 



1 Giacomini, quoted by Swale Vincent, Journ. Anat. and Phys. xxxviii. 1903, 

 p. 41. 



A 



Fig. 203. — Supra-renal and inter-renal bodies of Fishes. 

 A, of Scyllium catuhis ; B, of Acipenser sturio ; C, of 

 Pagdlus centrodontus. d.a, Dorsal aorta ; ir, inter- 

 renal body ; l.m, lymphoid portion of the mesonephros ; 

 m, mesonephros ; mtn, metanephros ; oes, oesophagus ; 

 sg.a, segmental arteries ; sr, supra-renal bodies ; sy.n, 

 sympathetic nerves. {From Swale Vincent.) 



