CHAPTER 3 



The Integument and Associated Structures 



A characteristic feature of the integument is the great development of the 

 cuticle, which covers the whole surface of the body. Even on those few 

 regions where a ciliated epithelium is developed, such as the dorsal ciliated 

 band of the metasoma and parts of the tentacles (pp. 33 and 79), there is still 

 a delicate cuticle. 



The epidermis 



The detailed structure of the epidermis varies, of course, both in different 

 species and in the different parts of the body in one and the same individual. 

 Almost always, however, the epidermis consists of epidermal cells, gland cells 

 and nervous elements, ganglionic and sensory cells, and more or less delicate 

 layers of nerve fibres. The epidermis lies on a basement membrane against 

 which abuts the circular muscle layer. 



The height of the epidermis and its richness in glandular and nervous 

 elements vary considerably in the different parts of the body. Some species, 

 chiefly the larger ones, are distinguished by the inordinate overall thickness 

 of the epidermis. The thickest epidermis is found on the cephalic lobe in the 

 protosomal region (Figs. 37, 38, 43), in the mesosoma (Figs. 29, 30, 39), and 

 also on the metameric region of the trunk (Figs. 33, 68) and in the post- 

 annular region (Figs. 22, 46). In the middle part of the trunk — that is, in the 

 males in the region of the strongly developed glandular region of the sperm- 

 ducts, and in the females in the hind region of the ovary where it is crowded 

 with large oocytes — the epidermis is usually grossly distended and attenuated 

 (Fig. 45), sometimes to the extent that it is a mere membrane (Figs. 61, 63, 69). 



The epidermis consists of cylindrical, more or less narrow cells, whose 

 nuclei are frequently all situated at the same level. The epidermal cells are 

 penetrated by numerous tonofibrillae which join the cuticle to the basement 

 membrane (Figs. 29, 38) (Jagersten, 1956; Ivanov, 1960a). 



Unicellular glands are particularly abundant on the front end of the body 

 and in general they are more weakly developed in the middle and hind parts 

 of the trunk. They are large goblet or tubular gland cells, more or less disten- 

 ded with secretion (Figs. 21, 27, 67). Amongst them may be distinguished 

 mucus glands, tubiparous glands [i.e. secreting the substances of which the 

 tube is formed] and albumen glands (Ivanov, 1960a). Only the tubiparous 



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