134 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. 



*' The nervous system of the cnistacea, submitted to their 



