ADRENAL BODIES 493 



may extend along the whole trunk and are primarily bilaterally 

 symmetrical : they constitute the bodies which in the lower 

 Vertebrates are known as the interrenal organ, and in higher forms 

 (Mammals) correspond to the so-called cortex of the adrenals. 

 The ectodermic portion arises at an early stage from the un- 

 differentiated rudiments of the sympathetic ganglia (or from 

 these and the chromaffin cells, cf. p. 247), and in lower Verte- 

 brates the resulting structures are spoken of as the suprarenal 

 organ, which corresponds to the medulla of the adrenal in Mammals. 

 The original distinction of these two components is plainly 

 retained in the lower Vertebrates throughout life, their union in 

 the higher types being of a secondary nature. 



Amongst Cyclostomes, the interrenal organ consists in the 

 Lampreys of small clusters of epithelial cells along the cardinal 

 veins, into the walls of which they extend as far as the lining 

 epithelium ; they are most markedly aggregated in the fatty 

 tissue lying between these veins and the aorta, and are also present 

 along the renal vessels. The suprarenal organ also consists of 

 epithelial tissue the constituents of which have the characteristics 

 of chromaffin cells : it extends along the parietal arteries arising 

 from the aorta, following their dorsal and ventral branches in the 

 body-walls, and also occurs between the aorta and cardinal vein 

 of either side, extending into the walls of the latter. The groups 

 of these cells may give rise to clusters (e.g. on the sinus venosus) 

 resembling those of Elasmobranchs and Amphibians ; and in many 

 places elements of the interrenal organ may occur amongst them, 

 without, however, uniting with them. Both interrenal and 

 suprarenal extend into the tail, mainly along the caudal artery 

 and vein. In the head the suprarenal alone is present, and is 

 situated along the jugular and parietal vessels, while in the 

 neighbourhood of the pronephric rudiments the interrenal alone 

 is found. 



In Elasmobranchs the two constituents also remain perfectly 

 distinct (Figs. 371 and 372). The suprarerials extend along the 

 whole body-cavity, and in Acanthias, Mustelus, and Galeus occur 

 regularly in every segment, while in others a fusion may take place 

 in many parts, resulting in an apparent reduction in number 

 (Rays). Their connection with the sympathetic ganglia is a very 

 intimate one. The fully-formed interrenal bodies consist of more 

 or less distinctly paired masses composed of cellular tubes or cords 

 and of blood-vessels, and may be connected with one another 

 in a longitudinal direction and also left and right. Fatty 

 particles enclosed within the cells give the organ a yellowish 

 colour. 



In Teleosts the suprarenals and interrenals are usually inter- 

 spersed amongst one another, and lymphoid cells always occur in 

 their neighbourhood. The suprarenals are related to the walls of 

 the cardinal veins especially the larger, right cardinal and are 



