NERVOUS SYSTEM 



71 



closely apposed ventral ganglia, the first pair of the 

 ventral chain. 



2. The ventral nerve-chain. 



Bemove the alimentary canal, from thepharynx backwards, 

 without i/njuring the nerve-collar and chain. 



'Eia. 25. — Lumbricus terrestris. A diagrammatic transverse section 

 through the middle of the body. On the left side of the figure a 

 nephridium is shown, and on the right side the setee. The septa 

 are not shown, and parts only of the circulatory system are repre- 

 sented, (a. m. m.) 



A, cuticle. B, epidermis. O, cffilom. OM, layer of circular muscles. 

 D, seta. DV, dorsal vessel. E, cavity of intestine. P, typhlosole, filled 

 with * hepatic * cells. G-, epithelium of intestine. H, ' hepatic * cells. 1, ventral 

 nerve-cord. J, nerve. K, * giant fibres.' L, nephrostome, liM, layer of 

 longitudinal muscles. M, the point where the nephridium perforates the 

 septum between two segments : between the two cut ends a considerable 

 length of very fine tube Ues, which is not shown in the figure. If, the first or 

 middle loop of the nephridium. 0» the second or inner loop of the nephridium. 

 F, the third or outer loop of the nephridium. B, external aperture of 

 the nephridium, SV, subneural vessel. V, intestinal vessel, "VV, ventral 

 vessel. 



