APHIPOUA. 217 



ORDER III. 



AMPHIPODA. 



The Amphipcda arc the only Malacrostraca with sessile and im- 

 moveable eyes, Avhose mandibles, like those of the preceding Crusta- 

 cea, are furnished with a palpus, and the only ones whose subcaudal 

 appendages, always very apparent, by their narrow and elongated 

 form, their articulations, bifurcations, and other incisures, as well as 

 by the hairs or cilia with which they are provided, resemble false or 

 natatory feet. In the Malacostraca of the following orders, these ap- 

 pendages have the form of laminee or scales ; here these liairs and 

 cilia appear to constitute the branchiae. Many of them, like the Sto- 

 mapoda and the Lcemodipoda, have vesicular bursae either between 

 their feet or at their external base, the use of which is unknown. 



The first pair of feet, or that Avhich corresponds to the second foot- 

 jaws, is always annexed to a particular segment, the first after the 

 head. The antennae, which with a single exception — the Phronima;, 

 — are four in number, project, gradually taper into a point, and consist, 

 as in the preceding Crustacea, of a peduncle and a single stem, or 

 one furnished at most with a little lateral branch, and usually com- 

 posed of several joints. The body is generally compressed and curved 

 beneath posteriorly. The terminal appendages of the tail are most 

 frequently styliform and articidated. Most of them swim and leap with 

 facility, and always laterally. Some inhabit springs and rivulets, and 

 are often found in couples consisting of the two sexes ; most of them 

 hoAvever live in salt water. Their colour is uniform, verging on 

 reddish or greenish. 



They may all be comprised in a single genus, that of 

 Ga.mmarus, Fab. 



Which we may subdivide, in the first place, into three sections, 

 from the form and number of the feet. 



1. Those which have fourteen feet all terminated by a hook, or 

 in a point. 



2. Those which also have fourteen feet, but which are — the four 

 last at least — simple natatory. 



3. Those which have only ten apparent feet. 

 The first section is divided into two. 



Some of them, — the Uroptera, Latr., usually have a large head ; 

 the antenna; are frequently short, and in some but two in number ; the 

 body is soft. All the feet", the fifth pair at most excepted, arc simple, 

 the anterior are short or small, and the tail is either furnished at the 

 extremity with lateral fins, or is terminated by points or appendages, 

 widened'and bidentated, or forked at their posterior extremity. They 



