INVERTEBRATA. 



337 



series of small stiff spikes, called setae. Of these there 

 are eight on each somite, in four double rows, in the 

 position shown by the transverse section in fig. 175. They 

 can readily be felt in a dead worm by gently passing it 

 through the fingers. By means of these the earthworm 

 can readily make its way over and through the ground. 



Fig. 175. TRANSVERSE SECTION OF HINDER REGION OF EARTHWORM. 

 (After Ho wee, altered.) 



Its burrowing habits are known to all, as is probably also 

 the fact that it very largely eats its way through the soil, 

 deriving nourishment from the decomposing plant-remains 

 in it. It also devours leaves. 



2. Skin and Body-wall. A transverse section of an 

 earthworm in the region behind the clitellum (fig. 175) 

 shows that there is a body-wall and an alimentary canal 

 separated by a ccelomic cavity. Thus it is as typically a 

 ccelomate animal as any of our Vertebrate types, but differs 

 from them in many important respects. 



The epidermis consists of a single layer of cells, among 

 which are numerous glandular cells, but no multicellular 

 glands. On its free surface is secreted a cuticle composed 

 ZOOL. 22 



