250 BRITISH ENTOMOSTRACA. 



is destitute of this recurved branch ; but it is otherwise 

 formed hke the three preceding. 



The thorax has been described above as occupying the 

 deep notch observable in the cai-apace. 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 wdiere 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 sm{dl 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, wdiere 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. 

 Inferiorly the stomach naiTOws 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 

 alidomen, 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 



