434 A. E. Yerrill — Marine Nernerteans of New JEnylatul, etc. 



a slender aiuil papilla. The posterior end is, however, seldom seen 

 entire, owing to its extreme fragility and its tendency to disrupt it- 

 self when irritated. When disturbed the middle region of the body 

 often contracts, while the anterior becomes thick and swollen. 



The increase in breadth of the body and enlargement of the mar- 

 ginal regions marks the commencement of the crowded lateral lobes 

 of the stomach and the genital organs, which can usually be seen 

 through the translucent integuments ; the caecal lobes of the intes- 

 tine usually appear as closely arranged, transverse, oblong spots, 

 forming a regular row along each side, from their commencement 

 nearly to the posterior end of the body, and usually having a slight- 

 ly darker or more brownish tint than the central and marginal 

 regions. The ctecal appendages, when seen from above or below, 

 usually appear as simple, narrow, but often forked, and closely ar- 

 ranged lobes, but when examined in sagittal sections they are most- 

 ly lobed and forked horizontally. The genital organs are closely 

 crowded between the enseal pouches of the stomach, digitally. 



The head is exceediugly changeable in shape, according to its 

 state of contractiou or expansion, but is usually narrower and thinner 

 than the adjacent part of the body. In full extension it is usually 

 broad spear-shaped or rhomboidal, and more or less pointed at the 

 ajsex, while marked lateral constrictions separate it posteriorly from 

 the body, but in another moment it may contract to a broad rounded 

 form, or it may even become deeply emarginate in front, with 

 rounded lateral lobes, or it may change to a very narrow and elon- 

 gated form with a sharp point. Ocelli are wanting. 



The lateral cephalic slits are large and deep, extending the entire 

 length of the head, and running forward close to and a little above 

 the proboscis-pore, those of opposite sides not uniting together ex- 

 cept by a very shallow furrow ; they do not join the proboscis-pore, 

 so that the snout is not four-lobed at tip, as in some allied species. 

 Their margins are thin and mobile, often undtdated or curled back 

 so as to open the slits widely and expose the deej) posterioi- pits, 

 which, in life, are dull red within. Proboscis-poi'e large, terminal or 

 subterminal. 



Mouth very large, but variable in form as the head varies in 

 shape, most frequently appearing as a long, narrow oval or oblong- 

 slit, its anterior end opposite the posterior ends of the lateral slits. 



Proboscis exceedingly long, slender, round, whitish, and, nearly 

 smooth. When the worm is placed in alcohol or other irritating 

 fluid the proboscis is usually ejected entirely without eversion (PI. 



