12 



THE PHYSIOLOGY OF EARTHWORMS 



a mucoprotein since Needham (1957) states that about 50% of the 

 nitrogen lost from the body is in the form of mucus protein. Ewer 

 and Hanson (1945) have shown that various epidermal cells stain 

 with mucicarmine and are metachromatic with thionin. In the 

 light of recent research on mucoproteins, on the occurrence of 

 chondroitin sulphate, and on the phenomenon of metachromasia 

 further knowledge of this secretion should not be long delayed. 



Cuticle 



The epidermal cells also secrete the cuticle which extends as a 



Fig. 4. Section of epidermis of Lumhricus terrestris. alb.c. 



albuminous gland cell; b.c. basal cell; cut. cuticle; m.c. mucous 



cells; B.C. supporting cells (from Stephenson, 1930). 



thin layer over the whole of the external body surface, and also the 

 fore and hind gut regions. It is an inert substance and can be 

 easily separated from the body wall, particularly if the animals are 

 killed by immersion in ether (Watson, 1958). 



In its chemical and physical properties the earthworm cuticle is 

 similar, but not identical, to the collagen of vertebrates. The first 

 demonstration that the cuticle is a typical fibrous protein was made 

 by Picken, Pryor and Swann (1947). Using X-ray diffraction 

 techniques they showed that the fibrous protein is embedded in a 

 matrix such that the fibres are orientated with one another. They 

 cross, making an angle of 90" with one another, and lie at 45° with 



