ZOOLOGY FOR MEDICAL STUDENTS CHAP. 



O 



Primitively the nephridial tube of the vertebrate opens at its inner 



by a tunnel-like nephrostome from the coelomic body-cavity or 



splanchnocoele. One of its primitive functions is to get rid of the 



tlui.l passed into that cavity by the coelomic lining. In correlation 



with this the portion of coelomic lining facing the nephrostome develops 



i\ increased powers of secreting coelomic fluid: it also becomes 



increased in area, bulging into the coelomic cavity as a rounded swelling 



t J K . glomerulus and receives a special blood supply, a branch from the 



aorta breaking up into a network in the interior of the glomerulus, in 

 Contact with the secretory epithelium. 



a.n.d 



FIG. 129. 



.in of renal tubule of vertebrate with its Malpighian body, a.n.d, Archinephric duct; 

 b.v, blood-vessels afferent and efferent ; gl, glomerulus, network of vessels closely ensheathed by 

 ; m.b, Malpighian body ; ns, nephrostome ; p, peritoneal cavity ; p.c, peritoneal 

 />./, peritoneal funnel ; /, tubule. 



In the case of the pronephros the glomeruli are very large and undergo 

 >n together, so that the group of pronephric tubules on each side has 

 a lar.LM- - (impound glomerulus projecting into the coelomic cavity towards 

 them. In the opisthonephros on the other hand the small individual 

 li remain separate and the portion of coelome immediately 

 one of them becomes more or less completely separated 

 from the main splanchnocoele. Consequently each glomerulus in the 

 opisthonephros is surrounded by a narrow space enclosed by a mem- 

 bra noii. wall, the whole constituting what is known as a Malpighian 

 body. Where a communication remains between the cavity of the 

 Malpiuhian body and the main splanchnocoele this communicating channel 

 ; lrd the peritoneal canal (Figs. 128, B, and 129, p.c} and its splanchno- 



opening the peritoneal funnel (Figs. 128, B, and 129, p.f). 

 Important changes also take place in connexion with the longitudinal 



