ORDER DECAPODA. 
145 
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 
01 less lively, and the colouring principle is decomposed in 
boiling water. But other combinations of this principle pro- 
duce m 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. XIII. r 
