204 CLASS CRUSTACEA. 



nisbed underneath, and which are analogous to those which 

 this part presents in the preceding Crustacea, but more diver- 

 sified here, and always, as it would appear, bearing gills, 

 differ in these respects, according to the sexes. The coupling 

 is the same as that of the insects. 



These animals are divided into three orders : those whose 

 mandibles are provided with a palpus, appear naturally to be 

 connected with the preceding Crustacea ; such are the amphi- 

 podes. Those in which these organs are without palpi, will 

 compose the following orders, the la^modipods and isopods. 

 Yamus, a genus of the second, being parasites, will conduct 

 us naturally to bopyrus and cymothoe, with which we shall 

 commence the isopods. 



THE THIRD ORDER OF CRUSTACEA. 



AMPHIPODA 



Are the only malacostraca with sessile and immoveable eyes, 

 whose mandibles, like those of the preceding Crustacea, are 

 provided with a palpus ; the only ones also whose subcaudal 

 appendages, always very apparent, resemble in their narrow 

 and elongated form, in their articulations, bifurcations, &c. 

 as well as in the hairs with which they are furnished, false 

 feet, or rather fin-feet. In the malacostraca of the following 

 orders these appendages have the form of laminae, or scales ; 

 these lashes or hairs appear here to constitute the gills. 

 Many exhibit, as well as the stomapods and laemodipods, ve- 

 sicular pouches placed between the feet, or at their external 

 base, of which the use is unknown. 



The first pair of feet, or that which corresponds to the 



