PYGOSPIO ELEGANS. 



191 



above the Looks, and another toward the ventral edge of the row, with a depression 

 between,- probably indicate the ventral lamella. 



In transverse section the anterior region agrees with the type of the Spionidse. The 

 dorsal longitudinal muscles taper toward the middle line, and at first the ventral longi- 

 tudinal are lateral in position, a wide interval with transverse fibres internally occurring 

 between them. Vertical fibres pass, as in other forms, from the dorsal to the ventral 

 margin, and a group of longitudinal fibres occurs on each side of the middle line within 

 the circular (transverse). The nerve-cords are at first wide apart in the hypoderm, but 

 they by-and-by come together in the mid-ventral line, and a neural canal occurs between 

 them in the anterior region. After the disappearance of the cephalic dorsal keel, the 



nc cvrri. 



Fig. 119. — Transverse section of the anterior region of Pygospio elegans, Claparede. Enlarged. 



mid-ventral region becomes prominent by the increase of the hypoderm (Fig. 119, hyp.), 

 which forms a thick layer outside the nerve- trunks. In this region transverse fibres still 

 bound the nerve-cords internally, and on the inner surface of these are the special longi- 

 tudinal fibres, between which and the longitudinal ventral muscles the vertical fibres 

 from the dorsum pass for insertion. 



The twenty-fifth foot presents a branchia as large as in front, with a broad, frilled 

 lamella externally. The dorsal setigerous process is a small conical papilla, from which 

 longer and more slender winged bristles than in front project. Four or five winged 

 hooks occur ventrally. Each foot has a series of glands forming a rounded mass with 

 refringent contents. 



Posteriorly the dorsal bristles greatly increase in length and slenderness, stretching 

 upward and outward as a hair-like tuft, whilst the superior lamella is represented by a 

 small conical papilla above their base. A slight rim indicates the ventral lamella, and the 

 hooks occupy the same relative position, but their number is greater, viz. about seven. 



