168 Mr. C. Spence Bate on the Nidijication of Crustacea. 



situated upou the antennae, they are so arranged that they can 

 pull themselves forwards. The antennae in Podocerus and Ce- 

 rapus are_, from their structm-e, evidently used as organs of pre- 

 hension ; and useful they are, no doubt, in their excursions 

 through the tangled maze of numerous zoophytes and forests of 

 weed that hang around the floating masses where they mostly 

 love to dwell. 



There can be little doubt, I think, that the hooks at the 

 posterior extremities of the animals enable them to retire into 

 their cases, and to turn round when they ax*e within, which they 

 do with a celerity that is noticeable. 



Those Amphipoda that inhabit hollows which they make by 

 burrowing into wood, clay, &c., such as Corophium and its near 

 allies, exhibit a marked distinction in their formation : they 

 penetrate by the aid of their anterior limbs. Thus we see 

 the inferior antennre developed into powerful (sometimes mon- 

 strous) organs, and used for breaking down the mud into which 

 they excavate, for the purpose, it is supposed, of feeding upon 

 the worms that dwell within it. In proportion to the power 

 given to the anterior part, by so much does the posterior ajipear 

 to be enfeebled. The posterior pleopoda in Corophium and Un- 

 ciola lose their importance, and in Cyriophium become rudi- 

 mentary. 



The distinct characters exhibited in the structure of this latter 

 subfamily (Coro/>/jM</£'5)ai-e of such importance, that it is impossible 

 to class the animals in the same group with Podocerus, although 

 there are certain similar features in their habits which have in- 

 duced authors to place them nearer to each other. Habit alone 

 cannot be trusted to define the position of an animal in relation 

 to its connexion with others of its class. 



Of this we have examples in Chelura and Phronima. The 

 former, like Corophium, burrows for food, but instead of pene- 

 trating into mud, eats its way into submarine wood; but its 

 structure is so anomalous M'hen compared with others of its class, 

 that every naturalist has thought it desirable to place it in a 

 family by itself. 



With regard to Phronima our knowledge is small : its habit is 

 that of an inhabitant of the gill-cavities of some one or more 

 species of Medusa ; but in the Collection of the British IMuseum 

 entrusted to my care for examination is a very curious case that 

 was sent home fromNaples by S. P. Pratt,Esq., as being the one in 

 which the animal was taken (PI. VIII. fig. 6). The structure is 

 thick, fleshy, semitransparent, and studded over the surface and 

 round the two orifices — one of which is smaller than the other — 

 with numerous white excrescences. Examination with the micro- 

 scope (tig. 6 a) shows the substance to be pervaded by bundles 



