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CLASS CRUSTACEA. 
FIRST CLASS OF ARTICULATED ANIMALS, AND 
PROVIDED WITH ARTICULATED FEET. 
THE CRUSTACEA (CRUSTACEA,) 
Are articulated animals with articulated feet, respiring 
through gills, covered in some by the edges of a testa, or 
carapace, external in others, but which are not inclosed in 
special cavities of the body, receiving the air through aper- 
tures placed at the surface of the skin. Their circulation is 
double, and analogous to that of the mollusca. The blood 
repairs from the heart situated on the back, to the different 
parts of the body, whence it comes back to the gills, and from 
thence it returns to the heart. These gills, situated sometimes 
at the base of the feet, or on the feet themselves, sometimes 
on the lower appendages of the abdomen, form either pyra- 
mids composed of plates piled together, or bristling with 
barbs, or tufts, with simple laminae, and even appear in some 
to be solely constituted by hairs. 
Some zootomists, and especially M. le Baron Cuvier, have 
made us acquainted with the nervous system of many Crus- 
tacea of divers orders. The same subject has lately been 
treated profoundly by MM. Victor Audouin and Milne Ed- 
wards, in their third memoir on the anatomy and physiology 
of animals of this class (Ann. des Scienc . Nat. xiv. 77,) and 
we want nothing to complete these researches but the publi- 
cation of those made by M. Straus, on the branchiopoda, and 
particularly on the limulae, of which these two naturalists 
have not spoken. 
<c The nervous system of the Crustacea, submitted to their 
