CRUSTACEA. 



When M. Cuvier published his arrangement of the Animal 

 Kingdom into four great divisions, he placed the Crustacea in 

 the third division, or that which included the Articulated Ani- 

 mals, placing before them in the same division the Annelides, 

 and after them the Arachnides and Insects; and M. Blainville, in 

 the endeavour to arrange the Crustacea according to their or- 

 ganization, suggested that they should go before the Mol- 

 lusca and Annelides, and after the Insects and Spiders, which 

 he conceived ought to follow in subordinate organization the 

 class of Fishes. But the arrangement of animals, considered in 

 regard to their organization, present difficulties not easily over- 

 come when an attempt is made to place them in one connected 

 and subordinate series ; and it has been already remarked, that 

 there appears to be in nature more than one series of animals, 

 which might with propriety be placed in parallel groups, or in a 

 double and relatively connected lateral series. The Crustacea, 

 in one view, ought certainly to occupy a more elevated place 

 among the Invertebral Animals than has been assigned to 

 them, above those, for instance, which are destitute of articu- 

 lated members and eyes, and where the sexual organs are in the 

 same individual ; but, on the other hand, to place them between 

 the Cephalopodous and Gasteropodous Mollusca, which would 

 seem to be their place in the series, would break the chain of 

 connection which unites this great class. It became necessary, 

 therefore, either to place the Crustacea before the Molluscous 

 animals or after them, and this last alternative has been adopted 

 by modern zoologists. 



The Crustacea, besides the characters they have in common 

 with the two following classes, possess some peculiar to them- 

 selves. They respire by branchiae, or by branchial laminae, 

 generally annexed to their feet or to their jaws. They have a 

 distinct heart provided with circulating vessels ; feet to the 

 number of five or seven pairs ; a head sometimes not distinct 

 from the trunk, with two or four antennae, and two moveable, 

 compound, and often pedunculated eyes. The organs of gene- 

 ration are at the base of the feet or at the extremity of the body. 



The Crustacea are in general to be recognized from their so- 

 lid envelope, which is sometimes extremely hard, as when the 

 calcareous matter of the covering predominates over the mem- 

 branous portion ; but, according to the families and genera, the 



