BY VKRA A. IRWIN-SMITH. 769 



head, and forming a semicircular fringe above tlie dorsal side of 

 the mouth-opening (Text-fig. 2, d.s.). These 'setae' probably 

 correspond to the hinder head-hairs described by Schepotiefi" 

 (7-8) for other species of Chcv.tosoina, but do nut correspond 

 in position with either the liinder circle of head-hairs or the 

 frontal head-hairs mentioned l)y him. Unmodified hairs, similar 

 to those on the rostrum, 0-022 to 0'026mm. long, occur on the 

 posterior part of the head, and appear to be arranged more or 

 less regularly in longitudinal rows. The cuticle of the rostrum 

 stops short of the extreme anterior end (Text-fig. 2, r.), leaving 

 a circular aperture through which the body-tissue projects in a 

 lip-like arrangement surrounding the mouth. On this, there is 

 a circle of very minute hairs or setae (Text-fig. 1, te.)^ apparently 

 six to eight in number, but, on account of the extremely small 

 size of all these parts, details are diflicult to determine with 

 accuracy. 



On either side of the rostrum, very close to the anterior 

 margin of the cuticle, there appears a curious cuticular marking 

 in the form of an open, spiral groove, the open end being 

 directed posteriorly (Text-figs. 1, 2, l.o.). Similar cuticular mark- 

 ings are mentioned by Metschnikofi:' (2) and Schepotief!"(7-8) as 

 occurring on all species of Chcetosoma hitherto recorded. Schepo- 

 tieff seems to think they are peculiar to the ChcKtosomcUid(t, and 

 compares them (7) with the wing-like head-appendages of the 

 Desmoscolecidce. But I have seen similar markings on some 

 small marine Nematodes, and Bastian has figured them in some 

 of the illustrations to his monograph on the Aiig7iillulidce{il), 

 notably on Comesoma vulym'is, though he does not mention them 

 in his description. De Man, in his ' Nordsee ]N'ematoden'(12), 

 also records them as occurring in Enoplus, Oncholaimus, AiUi- 

 comd, and Tri2yyloides, in conjunction with the " paired lateral 

 organs," which, he suggests, may be either excretory or sensory 

 in function. 8o far as I have been able to determine, they are 

 purely superficial cuticular structures. I cannot detect any .sign 

 of ducts leading away from them, nor any connection with the 

 deeper layers of the body. But it is possible that such connection 

 does occur, being difficult to detect on account of its extreme 

 minuteness. 



