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- 



O O / 



croscopical study of thin transverse or longitudinal sections. A 



m 



m 



^V^ .rtT^l 



'f^^W^^^': 



~ > ^ K 5 - "'^ > '' 



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

 mentary canal ; c, cuticle ; co% coelom ; c./>i, circular muscles ; c.r, circular vessel ; 

 c7.v, dorsal vessel; 7*y, hypodermis ; L/?J, longitudinal muscles; n.c, ventral nerve- 

 chain; p.e, peritoneal epithelium; 8, seta; s.g, setigerous gland; s.j.i% sub-intes- 

 tinal vessel ; s.m, muscle connecting the two groups of setae on the same side ; t y, 

 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. (beo-innin^ with the out- 



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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 



