250 
BRITISH ENTOMOSTRACA. 
is destitute of this recurved branch ; but it is otherwise 
formed like the three preceding. 
The thorax has been described above as occupying the 
deep notch observable in the carapace. Immediately 
.behind the suckers it becomes distinct from the head. It 
consists of four separate joints, from each of which arises 
a pair of the feet just described, and traces of a fifth are 
indistinctly visible. 
The abdomen, as in all the Siphonostoma, is very small. 
Most authors have described it under the name of tail, 
considering the thorax to be the abdomen. It consists of 
a broad plate, which at the base is bilobed, and carries, 
close to where the separation commences, a pair of rudi- 
mentary organs of an oval form, and ciliated on the mar- 
gins. 
In the female we see, at the base of each of these lobes, 
a small black, spherical body, which does not occur in the 
male. 
The intestinal canal commences at the base of the si- 
phonal tube, and extends to the bifurcation of the ab- 
domen, where it terminates by the anus. 
Upon viewing the little animal from above, we observe 
very distinctly, as has been already mentioned, a ramifica- 
tion of opaque tubes running through the lateral portions 
of the carapace (t. XXXI, f. 2). They arise from a single 
branch which springs from the stomach, and extends on 
each side to near the edge of the shell. 
The stomach, or commencement of the alimentary canal, 
is of considerable size, and of an oval form ; and these 
ramifications are considered by Jurine as the intestines. 
Interiorly the stomach narrows into a pyloric termination, 
which opens into a kind of caecum, having two appendages 
springing from its anterior part. This again contracts 
into the rectum, which descends to the bifurcation of the 
abdomen, and there opens by an oval orifice situated in 
the centre of the bifurcation. 
The female Argulus differs from all the other Siphono- 
stoma in not having like them external oviferous sacs. The 
