7654 Crustacea. 



their reach, just as artificial circumstances change the appearance 

 and physical condition. A ready example strikes us in the flat- 

 headed Indian. And Mr. Dilwyn, in his ' Contributions to a Natural 

 History of Swansea,' tells us how a dog, having got its nose cut with 

 a stone, ever after retained a cleft lip, a peculiarity that was exhibited 

 in all its after progeny, and only gradually died out in future gene- 

 rations. 



These floating crabs are generally pelagic, and found near the great 

 sargossan beds, which extend, pai'ticularly in the North Atlantic, on 

 every side, far beyond the distance that the eye can reach, like the 

 swathes of an immense ocean-prairie. 



Mr. Darwin, in his previously-quoted 'Naturalist's Voyage,' speaks of 

 one of these crabs as of a very remarkable structure : " It is allied to 

 the notopods (or those crabs which have their posterior legs placed 

 almost on their back, for the purpose of adhering to the under side of 

 the rocks). The penultimate joint, instead of terminating in a simple 

 claw, ends in three bristle-like appendages of dissimilar lengths, 

 the longest equalling that of the entire legs. These claws are 

 very thin, and are serrated with the finest teeth, directed backwards. 

 Their curved extremities are flattened, and on this part five most 

 minute cups are placed, which seem to act in the same manner as the 

 sucker on the arm of the cuttle-fish," As this animal lives in the open 

 sea, and probably wants a place of rest, I suppose this beautiful 

 and anomalous structure is adapted to take hold of floating marine 

 animals. 



But in Nature there is a wonderful distribution of animals, as if to 

 demonstrate to us how small a change in physical condition is neces- 

 sary to make apparently the same creature exist under directly 

 opposite circumstances. We have seen that some crabs live without 

 perhaps ever touching fixed ground ; so there are others that as seldom 

 enter the sea. The land crabs [Gegarcinas) of Jamaica and the 

 eastern Archipelago, exist many miles from the sea-shore, which 

 they only visit to enable the young to free themselves from their 

 egg-cases ; marching in a huge phalanx many deep, they instinc- 

 tively proceed to the nearest shore in a direct course and allovv no 

 obstacle to turn them aside from their path. For a short time the 

 young live in the sea, but ultimately they quit it for the land and live 

 in marshy districts where herbage is to be met with. A genus of East 

 India (Thelphusa) has been noticed by Bishop Heber, in his ' Indian 

 Journal,' to feed on grass and the young stalks of rice. The Deccan 

 swarms with them ; they burrow in the ground, whither they carry 



