SUPRARENAL BODIES. 511 
small cavity (Malpighian capsule) derived from the ccelom, 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 ccelom. 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 Miillerian 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 Miillerian 
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). 
Tn 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 Miillerian—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 coelomic 
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, é.g. constriction 
of the arterioles, and consequent heightening of the blood pressure, 
