268 INTERNAL SECRETION 



distinguished structurally by its lipoid cell contents and genetically 

 by its mesodermic origin in what is known as the interrenal zone. 

 During embryonal life, the interrenal system is extended over 

 large portions of the body, but as development progresses the 

 space which it occupies becomes more restricted. Principal bodies 

 are formed by the amalgamation of several suprarenal buds, by 

 regressive processes, and by the fission of single accessory bodies. 

 In the cyclostoma and in fish, the interrenal system remains at 

 this developmental stage. From the amphibia upwards, a large 

 portion of the interrenal system combines, at the next develop- 

 mental stage, with certain portions of the adrenal system to form 

 either a row of small bodies, as in the amphibia, or an isolated 

 organ such as the suprarenal of the amniota. In mammals and 

 more particularly in man, the principal mass of the interrenal 

 tissue is represented by the suprarenal cortex, while the structures 

 which were formerly regarded as buds split -off from the principal 

 organs, or as accessory suprarenals, are now known to be in- 

 dependent portions of the interrenal system, or accessory inter- 

 renals. 



Such accessory interrenal structures (see table, p. 137) are fre- 

 quently, though not constantly, found attached to the suprarenals 

 and forming part of them ; in the neighbourhood of the kidneys 

 and suprarenals; in the genital region the ligamentum latum in 

 the female (Marchand, Rossa), and the spermatic cord, epididymis, 

 and testicles of the male (Dagonet, Wiesel, Chiari) ; and occasion- 

 ally in other parts of the abdominal cavity. 



The accessory interrenals of the higher vertebrates have a 

 considerable structural similarity with the cortical substance of 

 the suprarenals. Occasionally these bodies possess all three 

 layers, though, as a rule, the two outer layers only are present. 

 In the earlier accounts of these organs, they are described as 

 having a medullary portion ; it is probable, however, that the 

 error arose from mistakes as to the identity of the innermost zona 

 reticularis. 



That the free portions of the interrenal system have a func- 

 tional significance is proved by the progressive development of the 

 split-off portions; by the compensatory hypertrophy of the so- 

 called accessory suprarenals in mammals, after removal of the 

 suprarenals (Stilling, Velich, Wiesel) ; by the compensatory hyper- 

 trophy of portions of interrenal bodies left in situ in Selachians 

 (Biedl) ; and by the survival of Teleostians after the removal of 

 all except their anterior cranial interrenal system (Giacomini). 



Experiments with the object of determining the function of 

 the interrenal tissue are, at the present moment, chiefly concerned 

 with that portion of the interrenal system which is represented 

 by the cortical substance of the suprarenal. There is no lack of 

 hypothesis, but the only fact supported by experiment which sheds 

 light upon the functional significance of the suprarenal cortex is 



