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CLASS CRUSTACEA. 
nished 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 kemodipods 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 laminas, or scales ; 
these lashes or hairs appear here to constitute the gills. 
Many exhibit, as well as the stomapods and kemodipods, ve- 
sicular pouches placed between the feet, or at their external 
base, ot which the use is unknown. 
The first pair of feet, or that which corresponds to the 
