156 



THE BIOLOGY OF AN ANIMAL. 



These six kinds of tissue constitute the main bulk of the 

 earthworm, as of higher animals generally ; but there are in ad- 

 dition other tissues which will be treated of hereafter. 



Arrangement of the Tissues. The simplest and most direct 

 mode of discovering the arrangement of the tissues is by the mi- 

 croscopical study of thin transverse or longitudinal sections (prac- 



':'; .'"lUi^y:- ; -?.%;'&. '-KuviiLi; flfifl ' 

 >A2L'l?i r -V-.^^'-^aaS^fe^-^^L- - - - 



FIG. 87. Transverse section of the body behind the clitellum. oe, cavity of the alimentary 

 canal; c, cuticle; cce, coslom; c.m, circular muscles; c.v, circular vessel: d.v, dorsal 

 vessel; hy, hypodermis; l.m, longitudinal muscles; n.c, ventral nerve-chain; p. e, peri- 

 toneal epithelium; s, seta; s.g, setigerous gland; s.i.v, sub-intestinal vessel; S.JH, 

 muscle connecting the two groups of setas on the same sido; ty, typhlosole. 



tical study, p. 171). A transverse section taken through the re- 

 gion of the stomach-intestine is represented in Fig. ST. Its 

 composition is as follows : 



A. Body-wall. 



This consists of five layers, viz. (beginning with the outside), 



1. Cuticle (c). A very thin transparent membrane, not com- 

 posed of cells and perforated by tine pores. It is a product or 

 secretion of the 



2. llijpodennis (hy) (epidermis or skin). A layer of colum- 



