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GENERAL ZOOLOGY 



certain general resemblance to the nephridial tubule of the 

 earthworm, in that both are segmental structures and both have 

 nephrostomal connections with the body cavity, though in the 

 frog this relation to the coelom is best shown in the embryo. 

 The uriniferous tubules of the frog's kidney lack nephrostomes; 

 but nephrostomes, no longer connected with tubules, are found 

 as ciliated funnel-shaped openings on the ventral surface of the 

 frog's kidney. These nephrostomes, strangely enough, have 

 become secondarily connected with renal veins into which they 



Fig. 95. — Diagram of glomerulus within capsule of uriniferous tubule, highly 

 magnified, a, afferent artery; e, efferent artery; t, tubule. The arrows show 

 the direction of blood flow. 



draw body fluid from the coelom. This relation is found only in 

 Salientia (Fig. 94). In other Amphibia and in the embryos of 

 Salientia, the nephrostomes are connected with the renal tubules. 

 The blind nephrostomal end of the uriniferous tubule of the 

 frog is provided with a double-walled capsule, enclosing a net- 

 work of blood vessels, known as a glomerulus, in close contact 

 with the inner wall of the capsule (Fig. 95). The outer wall of 

 the capsule continues as a tubule, which after following a twisted 

 course, during which it forms two loops, opens into a collecting 

 duct, running transversely across the kidney, near the dorsal 

 surface, from the inner margin to the ureter. The first loop of 



