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CLASS CRUSTACEA. 



The arrangement of the Crustacea in systems of natural 

 history has undergone numerous changes; they were 

 placed hy Linnaeus among the insects: — others consi- 

 dered them to have more analogy to the spiders/Lamarck 

 was the first who made the Crustacea an independent 

 CLASS forming two orders, which he has named after the 

 arrangement of the hranchise, or gills, by which they 

 breathe, namely, — the Crustacea hotnobranchiw, the dis- 

 tinguishing marks of which he describes in this manner ; 

 branchiae hidden under the lateral margins of a kind 

 of cuirass, covering the body of the animal, with the 

 exception of the tail ; the mandibles always furnished 

 with feelers, the eyes placed on footstalks, the head not 

 distinct from the trunk, and possessing ten feet to assist 

 them in their movements. Secondly, the Ci'ustacea 

 heterobranchiae, in which the branchiae are external, in 

 various situations, but never under the lateral margin 

 of a cuirass ; they are either under the belly or the tail, 

 adhering to the feet, or confounded with them : the eyes 

 are in general fixed, sedentary, not on foot-stalks. 



ORDER CRUSTACEA HOMOBRANCHIJE, 



{Shell-Fish with co7icealed gills.) 

 The first of these orders, the homobranchial Crustacea, 

 includes most of the larger kinds of shell-fish, as, for 

 instance, crabs, lobsters, and cray-fish ; shrimps and 

 prawns are also in this division. 



Their organization is much more perfect than that of 

 the other order, and, according to Lamarck, it is amon^ 

 these animals that the last appearance of the organ of 



