THE NEMERTIN1 



The integument of Nemertines consists of an epidermis resting 

 upon a basement connective tissue, which is usually thin, but in 

 Heteronemertini acquires a great thickness, and is then usually 

 invaded by the outer longitudinal muscles. The epidermis con- 

 sists of filamentous ciliated cells and gland cells of different kinds, 

 of these the most peculiar are " grouped gland cells " (see Figs. 

 VII. and XIV.), which are absent in Metanemertini. 



That characteristic Nemertine organ, the proboscis, occurs in 

 one of two conditions, as Johnston was the first to note ; it may 

 be unarmed, or it may be provided with calcareous stylets. In 

 the anoplous forms (viz. the Proto-, the Meso-, and Hetero- 

 nemertini) it is a cylindrical, muscular tube, closed at its hinder 



1 Fio. XIV. 2 



1, Epidermis of Drepanophorus crassus Quatrefages (from Perrier, after Burger). 6, basement 

 tissue ; e, epidermal filament cells ; si, goblet cells with mucous contents ; st, cells with 

 refringent, rod-like contents. 2, the integument of Eupolia delineata, D.Ch. (from Perrier, after 

 Burger). 6, basement membrane ; c, cilia; e, epidennal (filamentous) cells ; /, goblet cell; g, 

 connective tissue forming the cutis (in most Heteronemertines this cutis is invaded by the 

 outer longitudinal muscles) ; j, interstitial nuclei ; k, partitions between the groups of gland 

 cells ; I, subepidennal layer of longitudinal muscles ; m, subepidermal layer of circular muscles ; 

 p, packets of gland cells, sunk in the cutis ; r, radial muscle fibrils. 



end but open anteriorly; its wall becomes continuous with the 

 body wall at about the level of the brain. This precerebral 

 region is termed the " rhynchodaeum," and opens at the apex of 

 the head by a small round pore, the " rhynchostome." Behind the 

 brain the invaginated proboscis lies in a closed tubular cavity, the 

 " rhynchocoel," with muscular walls, to which it is attached, some- 

 where near the hinder end, by the retractor muscle (Fig. I. c, c'). A 

 transverse section of the proboscis shows the following layers of 

 tissue : internally (at rest) it is lined by tall columnar and gland- 

 ular cells, similar to those of the epidermis, from which, indeed, 

 this epithelium is derived during embryogeny ; these columnar 

 cells are arranged in groups and clusters, forming wart-like papillae 

 of various shapes and character, diagnostic of species. In most 

 genera these cells contain " rods " similar to the " rhabdites " of 



