TEANSVEESE SECTIONS. 



77 



A, Shape. 



The section is nearly circular in outline. The dorsal 

 surface is indicated by the typhlosole, the ventral by the 

 nerve-cord. 



B. The Integument. 



1. The cuticle is a thin structureless superficial layer, often 



I SV- 



FiG. 25. — Lumbricus. 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 setse. The septa are not shown, 

 and parts only of the circulatory system are represented, (a. m. m.) 



A, cuticle. B, epidermis. C, coelom. CM, layer of circular muscles 

 D, seta. DV, dorsal vessel. E, cavity of intestine. F, typlilosole, filled 

 ■with ' hepatic ' cells. G, epithelium of intestine. H, ' hepatic ' cells. I, ventral 

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

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

 septum between two segments ; between the two cut ends the convoluted 

 'narrow tube' is intercalated, which is not shown in the figure. W, the first 

 or long loop of the nephridium. O, the second or short loop of the nephri- 

 dium. P, the third or terminal loop of the nephridium. E, external aperture 

 of the nephridium. SV, snbneural vessel. V, intestinal vessel. W, ventral 



