THE NEMERTIN1 173 



Remarks upon the Class. The Nemertine worms usually live 

 under stones, or amongst sea-weed, or in empty mollusc shells and 

 similar places ; some even burrow in the mud or sand, and a few 

 secrete a tube of mucous material to which foreign substances 

 adhere (e.g. Carinella linearis, C. rubicunda, Valencinia longirostris). 

 The majority occur in shallow water, down to about 100 fathoms ; 

 only a few have been obtained from a greater depth, viz. Pela- 

 gonemertes, Nectonemertes, Hyalonemertes, and Carinina grata, at 1340 

 fathoms. These pelagic species, as well as Cerebi'atulus, spp., and 

 Drepanophorus, are characteristically Arctic. Eupolia is tropical. 

 The non-marine forms are exclusively Metanemertines, some 

 occur in fresh water, viz. Tetrastemma, sp. (13, 40), and Sticho- 

 stemma (31); others live on land, viz. Geonemertes, of which five 

 species have been described from various islands. A few live in 

 association with other animals, arid these again are Metanemertines, 

 with the exception of Cephalothrix galatheae, which is endoparasitic 

 in the ovaries of Galathea strigosa (12) ; others are ectoparasitic (3), 

 or perhaps only commensals, viz. Eunemertes carcinophila, Tetra- 

 stemma, spp., on Ascidians ; Malacobdella, in lamellibranchs (24). 

 The Nemertines are generally cylindrical worms of consider- 

 able length, but of small diameter, exhibiting a great degree of 

 contractibility ; some indeed attain an enormous length, e.g. 

 Linens longissima reaches a length of 8 or even 27 metres. 

 On the other hand, a few species of Tetrastemma, Oerstedia, and 

 Ototyphlonemertes are quite small. Euborlasia is an exception to 

 the designation "long," as it is short and sausage-shape, like a 

 Holothurian or Echiurid. Drepanophorus is relatively broad and 

 flat as is Malacobdella. Pelagonemertes (Fig. XL) is quite leaf -like 

 (32). The colouring is often bright and of various tints; patterns 

 are rare, either in the form of longitudinal stripes (Micrura), or 

 combined with circular rings of lighter tone or different colour 

 (Carinella). As a rule, the body presents no definite external 

 regions, nor is it segmented ; the hinder end is, however, generally 

 narrower than the rest of the body, and more pointed than the 

 anterior end which is truncated. In some of the Heteronemer- 

 tines (Cerebratulus, Micrura) there is a distinct " tail," having the 

 same structure as the body wall, but without gonads, and carrying 

 the anus at its apex. Only in a few cases (Carinella, Eupolia) is the 

 head definitely marked off from the trunk by a furrow (Fig. XXV.). 

 The mouth in the anoplous forms is some little distance from 

 the anterior end of the body, and is situated behind the brain ; 

 but in the Metanemertines it shifts forwards so as to lie in 

 front of this organ, and comes to lie close to the rhynchostome 

 in fact, in some species of Amphiporus, Malacobdella, and the Proso- 

 rhochmidae the two pores are coincident. The mouth leads into 

 a " foregut " or stomodaeum, which in the Anopla is a tube of 



