TRANSVERSE SECTIONS. 53 



and for this purpose transverse sections of the body are the 

 most instructive. Of these half a dozen or more should be 

 examined, as the appearances will necessarily differ according 

 to the particular organs and parts through which the section 

 happens to pass. * 



The following description is a general one, and will apply 

 to any section through the middle region of the body. 



A. Shape. 



A transverse section of the body of a leech is oval in out- 

 line, the transverse diameter being the greater, and the ventral 

 surface being flatter than the dorsal. 



B. The Integument. 



1. The cuticle. The most superficial layer is a thin struc- 



tureless elastic cuticle, which is secreted by the 

 underlying epidermis, and is shed and renewed at 

 frequent intervals during life. 



2. The epidermis consists of a single layer of columnar 



nucleated cells, wider at their outer than at their 



inner ends, 

 a. The epidermal glands. Certain of the epidermal 

 cells are modified to form unicellular glands. 

 These may remain in the epidermal layer as 

 mucous glands, or they may sink down into the 

 muscular layers, as in the case of the salivary 

 glands, and of the clitellar glands of the fifth 

 to the seventh somites, which latter secrete the 

 cocoon in which the eggs are laid. 



In all cases each cell is a complete gland in 

 itself, and preserves its communication with the 

 surface by means of a long slender ductule. 



3. The dermis is a layer of some thickness lying between 



the epidermis and the muscular coats. It consists of 

 a jelly-like matrix containing numerous branched 

 corpuscles. It is traversed by pigmented fibres, 

 which branch and anastomose very freely, and pene- 

 trate between the epidermal cells : to these the colour 



