CRABS. 



T57 



Brachyura,* or Crabs. These creatures are formed for pro- 

 gression on land, or at least for creeping on the bottom of the 

 sea. The tail, the great instrument of locomotion in the lobster, 

 is in the crabs reduced to a rudiment, and the fin at its extremity 

 entirely obliterated. The chclcz still continue to be the most 

 powerfully developed of the limbs, while the legs, now become 

 the principal locomotive agents, are either terminated by simple 

 points, as in those species which are most terrestrial in their habits, 

 or else, as in the swimming crabs, the posterior pair become ex- 

 panded into flattened oars, xiseful in natation. 



The habits of crabs are very various : some are exclusively 

 aquatic, and remain on the sands or rocks at great depths in the 

 sea ; others inhabit excavations formed in the soft coral reefs or 

 bars on certain coasts ; some spend their days altogether on a 

 shore, living in burrows or dens formed in a moist or boggy soil ; 

 others resort to the rocky flats or beaches to bask in the sun, 

 where only an occasional wave dashes over them, and seek refuge 

 in the sea when alarmed ; while some species are completely 

 terrestrial, inhabiting holes upon the highest hills and mountains 

 of the West Indies. 



The Spider Cr^bs (Ojcyrynchus)^ have their shells of a triangular shape, 

 narrowed in front into a point which almost resembles a beak. The legs are 

 long and very slender: this necessarily leads to slowness of motion; but they 

 are well fitted to a residence amongst rocks and stones covered with sea-weed, 

 among which they stride with little difficulty. In the winter they become 

 almost, if not altogether, torpid, concealing themselves at this season either in 

 deep crevices of rocks or embedded in the soil. These long-legged crabs are 

 frequently covered with sea-weeds, sponges, and other marine productions, 

 which so completely change their appearance that they are no longer recog- 

 nizable. Mr. Gosse observed at Ilfracombe the exuviation of a large' spider 

 crab which had retired into a crevice. When securing it he felt the body fall 

 away from the carapace, and on looking at the crab, found the new carapace 

 perfectly formed and coloured beneath it. The limbs and the under parts still 

 remained invested with their old shell. In a short time the hind legs wen- 

 freed, and then the animal extricated the front pair, tugging first at one and 

 then .at the other as if drawing off a pair of .boots. The parts had a jelly-like 

 softness, and seemed to be compressed as they were liberated by the fluids 

 being forced back so as to distend the freed portion of the limb. Mr. Gossc 

 did not observe any struggling it seemed a very simple and easy matter. 

 The new integuments were complete, though soft, before the old were torn off; 

 and the immediate cause of the separation of the crust appeared to be the 

 sudden growth of the animal within forcing asunder the upper and lower shells 

 at the posterior margin. 



The Swimming Crabs (Pinnipcdes) % have the hinder feet terminated by 



s, brachys, short; ovpa, oura, a tail. t o^s, oxys, sharp; pvvxos, rhynchos, 

 a snout. + Pinna, a featJier or leaflet ; pes, pedis, afoot. 



