ARRANGEMENT OF TISSUES. 



91 



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. A 



,c 



FIG. 39. Transverse section of the body behind the clitellum. a.c, cavity of the ali- 

 mentary canal ; c, cuticle ; car, coelom ; c.m, circular muscles ; c.r, circular vessel ; 

 cf.r, dorsal vessel; /[/, hypodermis; Lm, longitudinal muscles; n.c, ventral nerve- 

 chain; p.f, peritoneal epithelium; s, seta; .(/, setigerous gland; s.i.r, sub-intes- 

 tinal vessel ; s.m, muscle connecting the two groups of setse on the same side ; ty, 

 typhlosole. 



transverse section taken through the region of the stomach- 

 intestine is represented in Fig. 39. Its composition is as 

 follows : 

 A. BODY-WALL. 



This consists of five layers, viz. (beginning with the out- 

 side), 



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

 composed of cells and perforated by fine pores. It is a product 

 or secretion of the 



