78 THE EARTHWORM. 



separated by the action of the reagents from the 

 underlying epidermis. 



2. The epidermis lies immediately below the cuticle. It 



consists of a single layer of columnar cells, set side 

 by side at right angles to the surface, with nuclei 

 near their bases. Many of these cells have the 

 character of 'goblet cells,' being distended by a 

 granular secretion formed within them ; other cells 

 lying between these are extremely slender. In the 

 clitellum the epidermis is greatly thickened. Blood- 

 vessels penetrate between the epidermal cells. 



3. The dermis is an exceedingly thin layer immediately 



beneath the epidermis. 



4. The setae are lodged in sacs, which are invaginations of 



the skin extending deep into the body, through both 

 the muscular layers. They are euticular structures, 

 and are moved by special muscles. Setae in various 

 stages of development may be seen within the sacs. 



C. The Muscular Layers of the Body-wall. 



1. The external layer, which is rather thicker than the 



epidermis, consists of transverse fibres running round 

 the body : it is completely interrupted at the grooves 

 between the segments. The connective tissue between 

 the muscle-fibres is pigmented slightly : in the dorsal 

 wall of the (Esophageal region this pigmentation is 

 very marked. 



2. The internal layer is very much thicker than the ex- 



ternal. It consists of longitudinal fibres, arranged 

 on the sides of a series of radial longitudinal sheets,, 

 and having a feather-like appearance in transverse 

 section. 



D. The Coelom, or Body-cavity. 



This is the space around the intestine, between it and the 

 body-wall. It is lined by a thin peritoneal epithelium, and 

 contains a colourless fluid, with numerous amoeboid corpuscles. 



