ETEONE. 



99 



with a rounded thick inferior border on each side ; whilst the ventral have a tendency 

 to a crescentic arrangement of each mass, for the outer border (in section) curves 

 inward dorsally. 



The alimentary canal has a thick coat of longitudinal muscular fibres exteriorly — 

 apparently only a basement-membrane with a few circular fibres intervening between 

 it and. the nucleated outer cellular layer. 



The oblique muscles are of great strength, and thus in section the ventral median 

 line is deeply grooved. They meet in the mid-ventral line in Eteone spetsbergensis, but 

 they show intervals in E. picta. The nerve-area is thus generally pushed further inward 

 than in Phyllodoce, and both trunks and ganglia have a firm sheath with longitudinal 

 fibres. The interganglionic cords are separate. At intervals strong transverse bands 

 of muscle pass above the cords from side to side. The circular muscular fibres are 

 largely developed in the dorso-lateral regions. 



Ehlers (1864) characterises the genus thus: Body elongated; head with four 



dv 



Fig. 43. — Section of Eteone spetzbergensis, to indicate the muscles. The same letters are used as formerly. 



tentacles ; two pairs of tentacular cirri ; segments similar with simple feet ; dorsal cirrus 

 small, leaf-like, with the base resting on the dorsum, much larger than the ovate ventral 

 cirrus; two leaf -like anal cirri. Claparede (1868) includes Mysta in this genus, as also 

 does Levinsen (1883). 



Grube (1879) mentions that the tentacular cirri are short, as also the tentacles, 

 which are only a third the length of the short trapezoidal head. Some genera lose 

 the dorsal cirri in the second segment. In others segment 1 has one tentacular cirrus, 

 segment 2 also one. Eyes small, often mere points, and frequently disappear in spirit. 

 Proboscis with two cordate papillge ; upper surface smooth, or covered with pointed 

 papilla, or ringed, or with sparsely distributed papillae having minute processes (hook- 

 like). Body does not show metallic lustre, and when coloured has specks. Small as 

 a rule; characteristic of northern and arctic seas and sparingly distributed. 



Grube groups the species of Eteone as B. — tentacular cirri on first segment; B s . 



only one pair of eyes. 



(a) Head as broad or broader than long. E. arctica, E. picta, E. flava. 



(b) Head more or less longer than broad. E. longa, E. pusilla, E. spetsbergensis. 

 Gravier 1 mentions a strong band of transverse muscular fibres from side to side 



1 ' Bull. Sc. Fr. Belg./ t. xxix, p. 368, pi. xvii, f. 13. 



