ORDER DECAPOD A. 115 



are nevertheless obliged to make their sojourn in burrows, or 

 in fresh and humid places. The nature of the decapod 

 Crustacea, is voracious and carnivorous. Certain species 

 even proceed to cemeteries to devour carcases, and to feed on 

 them. Their limbs are regenerated with great rapidity, but 

 it is necessary that the fractures should take place at the 

 junction of the articulations, and they know how to cause 

 them there, if the breach should accidentally occur elsewhere. 

 When they are desirous of changing skin, they seek a retired 

 place, so as to be in shelter from the pursuits of their enemies, 

 and to remain there in tranquillity. When the moulting is 

 done, their body is soft, and, according to some persons, is 

 then of a more delicate flavour. From a chemical analysis of 

 the old testa, we learn that it is formed of carbonate and 

 phosphate of lime, united in divers proportions to gelatine. 

 On those proportions depends the solidity of the testa. It is 

 much less thick and flexible in the last genera of this order, 

 and farther on it becomes almost membranaceous. M. de 

 Blainville has observed, that that of the palinuri is composed 

 of four superposed strata, of which the two lower ones, and 

 the upper are membranaceous ; the calcareous matter is in- 

 terposed between them, and forms the other stratum. From 

 the action of heat, the epidermis assumes a tint of red, more 

 or less lively, and the colouring principle is decomposed in 

 boiling water. But other combinations of thisfprinciple pro- 

 duce in some species, a very agreeable mixture^ of colours, 

 often bordering on blue or green. 



The greater number of fossil Crustacea, which have been 

 discovered up to the present day, belong to the order of de- 

 capods. Among those of Europe, some, and the most ancient, 

 approach the species now actually existing in the zones 

 which neighbour the tropics. The others, or the more modern, 

 have a great affinity with the living species, which are proper 



VOL. xm. L 



