376 Proceedings of the Royal Society 
developed in this species, and their terminations over the cords 
can only be seen occasionally. Each cord has a neural canal at 
its upper third, near the middle line. Glycera Goesi, Mgrn., shows 
nearly the same arrangements ; while G. setosa , (Erst., exhibits 
more evident separation of the cords. The insertions of the oblique 
muscles over the nerve-area are best seen in G. alia , Rathke, a 
large species, in which the cords are proportionally less. 
Ariciid.®. — In the anterior region of Aricia latreillii , Aud. 
and Ed., the cords are situated at the upper part of a somewhat 
triangular hypodermic area, bounded laterally by that part of the 
circular coat clasping the ventral longitudinal muscles. Powerful 
oblique muscles meet for insertion over each cord. In the same 
region of Scolopos armiger , 0. F. Muller, the cords also lie beneath 
the point of union of the greatly developed and nearly horizontal 
oblique muscles, and supported laterally by the massive edges of 
the ventral longitudinal. A single neural canal exists superiorly. 
Between the cords and the hypoderm is the thick circular muscular 
coat. In the middle of the body the nerves are thrust upward by 
the great ventral muscles, which are only separated by the narrow 
pedicle of the area. 
OpheliiDjE. — Throughout the greater part of Ammotrypane 
aulogaster , H. R., a peculiar modification of the body-wall exists, 
in the form of a constriction between the dorsal and ventral longi- 
tudinal muscles. The intermediate pedicle is formed apparently 
by the metamorphosed vertical muscles, which have coalesced over 
the nerve cords. The oblique muscles pass from the outer edge of 
the ventral longitudinal to the middle line below the nerve-area. 
A small and indistinct neural canal appears toward the upper part 
of the latter. In Ophelia limacina , H. R., the cords in the smoothly 
rounded anterior third lie in the middle of the long interval 
between the ventral longitudinal muscles. The oblique are in- 
serted far outside the cords. Externally are a granular area, a 
series of transverse fibres, and the cuticle. Toward the posterior 
part of the body, where the ventral ridges are well-developed, the 
cords, by an intricate change in the relationships of the muscles, 
get above the median (ventral) insertion of the vertical, the fibres 
of which extend outward and somewhat downward into each pedicle. 
The true oblique is with difficulty seen ; but it appears to be a 
