Title: Animal biology
Identifier: animalbiology00wood (find matches)
Year: 1938 (1930s)
Authors: Woodruff, Lorande Loss, 1879-1947
Subjects: Biology; Zoology; Physiology
Publisher: New York The Macmillan company
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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EXCRETION 185 the coelom and the outer world, and affording a path of egress for the waste matter in the coelomic fluid. But in addition, the blood vascular system carries nitrogenous waste, inorganic salts in solu- tion, etc., to the coiled part of the nephridial tube where special cells take them from the blood and deliver them to the interior of the tube to be passed out of the body. Thus the nephridia of the Earthworm remove waste material from both the coelomic fluid and the blood. Artery Vein Although the primitive /* "x \* ^ segmentation of the coe- / \ . lorn has disappeared in ' the Vertebrates, neverthe- less there are good grounds for believing that the ancient, segmentally ar- ranged nephridia are the basis of the essential excre- tory elements of the kid- neys. Thus in the lowest Vertebrates the primitive type of kidney, or pro- nephros as it is called, con- sists of a series of segmen- tally arranged nephridia in the dorsal part of the ante- rior end of the coelom. These, however, instead of opening independently to the exterior, discharge their products into a common tube (PRONEPHRIC DUCT) lit—Urethra which passes them to the Fig. 130. — Diagram of the human urinary outside. In higher forms system, posterior view. See Fig. 134B. the pronephros disappears, and its function is taken over by an- other series of nephridia which appears in the coelom posterior to the pronephros. This series constitutes the mesonephros, and opens into the pronephric duct which accordingly now is called the mesonephric duct. Finally, in still higher Vertebrates this second urinary organ is replaced by a third, the kidney proper (metanephros) and its special duct, the ureter. (Fig. 129.)
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