SUPRARENAL BODIES. b ii 



small cavity (Malpighian capsule) derived from the coelom, and con- 

 taining a mass of capillaries which project into the cavity of the 

 tubule ; and (3) a coiled tube in part excretory, in part a conducting 

 canal for the waste filtered from the blood. The metanephric 

 tubules have a quite similar structure, but the nephrostome is never 

 present. 



In all Vertebrates the primitive nephridia open into a 

 pair of longitudinal ducts, developed like the nephridia as 

 special portions of the coelom. These ducts open into the 

 end of the gut. According to their connections with the 

 nephridia these longitudinal ducts are called pronephric, 

 mesonephric, or metanephric ducts, and they are also called 

 segmental ducts. In Elasmobranch fishes a Mullerian duct 

 is separated off from in front backwards from the 

 longitudinal duct and forms the oviduct of the female, a 

 rudiment in the male. After the separation of the Mullerian 

 duct, the longitudinal duct (now called mesonephric or 

 Wolffian) forms in the male the vas deferens and also 

 receives the tubes from the permanent kidney (mesonephros). 

 In the female the Wolffian duct has this last function. In 

 general it may be said that the original longitudinal duct 

 becomes the vas deferens in the male Vertebrate, and that 

 another duct the Mullerian whose development is obscure 

 except in Elasmobranchs, forms the oviduct. The meta- 

 nephric duct, developed in part from the hinder end of the 

 mesonephric duct, is the ureter of the permanent kidney in 

 Amniota. 



Suprarenal bodies. These are found in most Vertebrates near 

 the reproductive organs and kidneys. They seem to increase in 

 importance as we ascend the series. Typically, each shows a dis- 

 tinction into a cortical and a medullary zone. It is usually asserted 

 that these two areas have a different origin, the medullary region being 

 derived from the sympathetic nervous system, the cortex from the ccelomic 

 epithelium. There is much evidence (morphological and physiological) 

 that the suprarenals of Elasmobranchs correspond to the medullary part 

 in Mammals, while the interrenals of Elasmobranchs and the suprarenals 

 of Teleosts and Ganoids correspond to the cortical portion in Mammals. 



With regard to function, there is some uncertainty. The suprarenal 

 bodies are relatively very large in embryonic life, but fail to maintain 

 their primitively rapid rate of growth. A substance, adrenalin, can be 

 extracted from them which has a remarkable action upon the parts 

 innervated by the sympathetic system, producing on injection the same 

 effects as stimulation of the sympathetic would have, e.g. constriction 

 of the arterioles, and consequent heightening of the blood pressure. 



34 



