128 Proceedings of the Royal Society 
cavity which forms therein is superiorly a small group of longitu- 
dinal fibres. 
Behind the foregoing a transverse dorsal layer is found beneath 
the central and now solid hypodermic process, next the dorsal lon- 
gitudinal muscles (the fasciculi of which, in the middle line, are 
directed downward and outward, while the outer are directed down- 
ward and inward); then a kind of X shaped process occurs in the 
centre, the legs of the X being prolonged horizontally, so that the 
whole resembles a figure of oo, the two spaces containing muscular 
fasciculi. The lateral and oblique muscles are largely developed, 
the latter having the nerve-cord on each side below its ventral 
attachment. 
The most interesting point in this form, perhaps, is the structure 
of the fifth body-segment, which bears the remarkable hooks 
characteristic of the genus, besides peculiar bristles with spear- 
shaped heads, and a minute fascicle of the ordinary structure. 
Immediately in front of the hooks, the body in transverse section 
shows externally a circular coat, which is thin at some parts, but 
greatly developed at others. Dorsally a very powerful series of 
fibres spread outward from the middle line on each side — some be- 
coming continuous with the circular coat, others passing obliquely 
outward and downward to the superior bristle-bundle. Inferiorly 
a strong transverse band lies over the nerve-trunks, and forms an 
external investment to the ventral longitudinal muscles. The 
oblique muscle comes from the lower bristle-bundle, and joins the 
former over the nerve-trunk, after piercing the vertical bands. 
The superior longitudinal muscle forms a great mass on each side, 
and it interdigitates with the fibres of the vertical muscle. The 
latter is greatly developed, especially at its inner border, next the 
oesophagus. The same (vertical) fibres pierce the ventral longitu- 
dinal muscle in the compartment formed for it by the circular and 
oblique bands. The size of the ventral is less than that of the 
dorsal longitudinal muscles. A somewhat strong group of longitu- 
dinal fibres lies within the ventral transverse band. Finally, each 
fascicle of the ordinary bristles has a V shaped series of fibres 
extending from the base of the tuft to the lateral wall, and inter- 
digitating with those from the transverse and other muscles of the 
region. 
