XEPHTHYS. 



Genus XXIX. — Xephthys, Guvier, 1817. 



Head as in the family ; both tentacles present. Rarely with a pair of eyes. Pro- 

 boscis of two regions, with 22 distal rows of papillse in extrusion, a double arch of bifid 

 papillse round the aperture, and a pair of horny teeth internally. Body and feet as in the 

 family. Foot with the dorsal and ventral cirri either conical or foliaceous. LamellaB 

 generally well developed. Bristles of two kinds, shorter barred bristles anteriorly in each 

 division, and elongated forms with a flattened though narrow blade serrated at the edge 

 (from minute rows of spikes) behind. From the formation of the foot they all occur on the 

 anterior surface. Xerve-cords in the typical position. Segmental organs as in the family. 



In JSfephthys cseca the dorsal muscles fuse in the middle line which is only distinguished 

 by being the thinnest part of the sheet. They widen on each side and end in transverse 



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11 : (i i - '."• •' -" " ••' ■ .- " 



orti 



Fig. 37. — Magnified view of the nerve-area of the ventral cord of Nephtliys cseca. The fibres of the oblique 



muscles (o.m.) occur below. 



section in an outer flap quite free from the thin circular layer of the region. From the 

 shelving outer edge of the longitudinal layer on each side to the border of the foot two 

 series of powerful fibres are conspicuous. The first is a horizontal layer which 

 commences as a narrow continuation of the circular and passes outward in a somewhat 

 fusiform manner to the dorsum of the foot. The second assumes the form of strong 

 oblique bands which slope from above downward and outward from the dorsal edge to 

 the foot. Besides these a separate longitudinal band occurs at the shelving tip of the 

 great dorsal layer. 



The ventral longitudinal muscles form, in transverse section, two large ovoid masses 

 on each side of the median nerve- cords. They are bounded externally by a strong band 

 of oblique fibres from above, whilst superficially they have the cuticle, hypoderm, and 

 some circular fibres. 



The fasciculi of both dorsal and ventral longitudinal muscles have their long axes 

 directed inward, and thus a somewhat radiate aspect is given to the transverse sections. 



The nerve-area in the centre is shaped somewhat like an inverted crown, the convex 



