3. THE INTEGUMENT AND ASSOCIATED STRUCTURES 



33 



glands are found along the whole length of the body. Spindle-shaped 

 secretory bodies with longitudinal striations are found in the unicellular 

 tubiparous glands of the mesosoma (Jagersten, 1956). These cells also con- 

 tain granular masses of secreta which give a positive reaction for poly- 

 saccharides (Fig. 21) (Ivanov, 1960a). Only in a few spots does the epidermis 

 assume a continuous glandular nature. 

 Thus a strong concentration of glands is 

 found in the tall epithelium at the tip of 

 the cephalic lobe. In many species of 

 Siboglinum the epidermis behind the 

 bridle is remarkable for its richness in 

 unicellular glands with granules of a 

 seemingly proteinaceous or albuminous 

 secretion ; here they may form a glandu- 

 lar girdle, usually incomplete (Fig. 6), or 

 longitudinal glandular ribbons along the 

 mesosoma (in S. taeniaphorum and S. 

 atlanticum). In the nonmetameric region 

 of the trunk aggregations of gland cells 

 are frequently encountered forming 

 thickened areas of integument. Finally, 



there are the very characteristic dorsal glandular shields of the Athecanephria, 

 arranged metamerically in the postannular region of the trunk (Figs. 8, 14). 

 Each shield consists of very large gland cells whose secretion takes the form 

 of rather large rounded granules (Fig. 22). 



The layer of nerve fibres lying between the basal ends of the epidermal and 

 gland cells and the underlying basement membrane can scarcely be regarded 

 as an essential constituent of the epidermis per se, yet it is invariably found 

 there (Figs. 27, 29, 38). In definite places, which seem to be the central parts 

 of the nervous system or its main paths of conduction, the nerve layer reaches 

 a particularly strong degree of development (Ivanov, 1956b). 



The cells of the epithelial dorsal ciliated band (Fig. 23) are furnished with 

 dense and comparatively short cilia. In spite of this the epithelium of the tract 

 is covered, in the majority of species, with an extremely thin but distinct cuticle 

 under which lie the rows of basal granules of the cilia. In each cell the cone 

 of root-threads of the cilia, with the apex towards the nucleus, may readily be 

 seen. There are no gland cells in this region, but the nervous elements are 

 well developed, possessing both a layer of nerve fibres and of ganglionic cells. 

 In S. caulleryi the ciliated band appears to have lost its cilia (Fig. 33). 



50ji 



Fig. 21. Single-celled glands in the 

 epithelium of Lamellisabella zachsi, 

 stained for polysaccharides, eg - group 

 of unicellular glands with granular 

 secretion ; cut - intensely stained cuticle ; 

 mb - basement membrane. (After 

 Ivanov, 1960a.) 



