290 CLAUS^ ON THE 



into a kind of pincers, by the insertion of a moveable seta at 

 tlie base of a styliform process on the terminal joints. Van 

 Beneden has also noticed this pair of appendages correspond- 

 ing to the inner antennae, but has described it as the first 

 pair of jaw-feet, following Milne-Edwards. {' Ann. d. Sc. 

 Nat./ torn, xxviii, '^ Sur I'Organisation delabouehe chez les 

 Crustaces su9eurs.") The oral organs were very correctly 

 understood by Rathke, although that observer was unable to 

 obtain a satisfactory view of their form, and consequently has 

 given no figure of them, as he himself states. They repre- 

 sent, as was first recognised by Rathke and Van Beneden, a 

 suctorial proboscis, to which succeed two pairs of clasping 

 organs, representing the jaw- feet. The suctorial proboscis 

 (fig. 4), as compared with the corresponding parts of the 

 mouth in the Siphonostomata, appears short, and compressed 

 into an acetabuliform organ, in which I have in vain sought to 

 trace its original composition out of a labium and labrum, as 

 can be so readily made out in Pandarus, Nogagus, and 

 Caligus. I must particularly state, that the more intimate 

 relations of this svictorial disc have not been rendered perfectly 

 clear; all that I can assert positively is, that two pairs of 

 appendages are concerned in it — two serrated jaws (fig. 4 c) 

 and two setigerous palpi (fig. 4 d). The former appear to be 

 curved at an obtuse angle, and in the skeleton are affixed by 

 peculiar chitinous rods, which project symmetrically on the 

 sides of the acetabulum, below which they are united by an 

 arched, horny piece (fig. 4). The palpus is inserted next to 

 the piercing seta ; it is also based on a firm, chitinous rod, 

 and appears as a single-jointed papilla, which, together with 

 several short points, supports two considerable- sized curved 

 setae. The two pairs of jaw-feet occupy the loAver half of the 

 cephalic portion, and they are separated from each other by 

 hard skeleton-plates, of a defined symmetrical form. Those 

 of the first pair are constituted of two joints, and. support at 

 their apices two strong clasping-hooks ; whilst the second, as 

 I, in contradiction to Rathke and Van Beneden, must assert, 

 is five-jointed. The last three joints, furnished each with a 

 hook-like seta, might easily, it is true, be taken for a single 

 joint, particularly in the female, in which it is only under a 

 strong magnifying power that they can be recognised as 

 distinct. 



With respect to the constitution of the other limbs, and 

 the structure of the abdomen, I shall reserve what I have to 

 say for a more detailed account, since the figures here given 

 will suffice to show the peculiarities. 



