33^ 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



coelomic fluid into the tubule and thence outward. Farther along 

 the tubule expands into a Malpighian or renal corpuscle (fig. 360), 

 This consists of a vesicle (Bowman's capsule), one side of which 

 projects into the other, nearly filling the cavity. This inturned por- 

 tion is the glomerulus. It consists of a network of capillary blood- 

 vessels — a rete mirabile — supphed by an artery and drained by a 



Fig. 359. — Diagram of conventionalized excretory tubule, a, ascending limb of 

 Henle's loop; b, Bowman's capsule of Malpighian body; c' — c^, first and second con- 

 voluted tubules; ct, collecting tubule; d, descending limb of Henle's loop; g, glomerulus 

 of Malpighian body; with artery and vein; h, Henle's loop; n, nephrostome opening 

 into ccelom; x, entrance of other tubules into collecting duct. 



vein. Beyond the connexion with the Malpighian body the tubule 

 becomes contorted or convoluted and its cells are strongly glandular 

 in character. This first convoluted tubule is succeeded by a nearly 

 straight tract, folded once on itself into the descending and ascending 

 limbs of Henle's loop. Next follows the second convoluted tubule, 



Fig. 360. — Diagram of renal (Malpighian) corpuscle, o, artery; b, Bowman's capsule; 

 gl, glomerulus; n, nephrostome; t, nephridial tubule; », vein. 



which passes by means of a short connecting tubule into a non-glandu- 

 lar collecting tubule into which several other systems of excretory 

 tubules enter, and which leads more or less directly into the urinary 

 duct which conveys the waste from the excretory organ to the exterior. 

 One or another of these typical parts may be lacking in certain 

 groups. Thus in the amniotes the nephrostomes are never formed, 



