334 W. BLAXLAND BENHAM. 



(under high power), b. v. Blood-vessels, cocl. ep. Nucleus of flat coelomic 

 epithelium, cone. Coloured concretions in the vesicular renal cells (epith.). 

 n. Nucleus of these cells, ezc. pr. A granular coagulum, probably excretory 

 product in nephridium. 



Fig. 42. — Diagram to illustrate the suggested evolution of a single nephri- 

 dial tube from an aggregation of a group of plectonephric tubules, a. A 

 portion of primitive network of a segment, b. One of the many funnels 

 occurring in each segment (as in Perichseta). c. One of the numerous 

 ducts passing to exterior, b'. One of the funnels which persists and has 

 become increased in size by addition of marginal cells, c'. The ultimate 

 single duct. e. The tube (darkly shaded) of meganephric condition. /. A 

 few of the anastomoses (dotted) remaining, as in Brachydrilus, &c. 



