330 CLASS CRUSTACEA. 



segment immediately preceding the sexual organs, and which, 

 in the females, supports two appendages in the form of little 

 feet {fulcra, Jurine), may be considered as the first of the 

 tail, which is not always very exactly distinguished from the 

 thorax. It is formed of six segments or articulations ; the 

 second supports, underneath, in the males, two articulated 

 appendages, sometimes simple, sometimes having, at the 

 internal side, a small division, or branch, of various forms, 

 and constituting wholly, or in part, the organs of generation. 

 The vulva is situated, in the other sex, on the same articula- 

 tion ; the last is terminated by two points, or stylets, forming 

 a fork, and more or less furnished with setse, or penniform 

 filaments. The other, or anterior portion of the body, is di- 

 vided into four segments, the first of which, much the largest, 

 composes the head and a portion of the thorax, which are 

 thus covered by a common scale. It supports the eye, four 

 antennae, two mandibles {internal mandibles, Jurine), fur- 

 nished with a simple palpus, or divided into two articulated 

 branches, two jaws (external mandibles, or labrum with bar- 

 bies, Jurine), and four feet, each divided into two cylindri- 

 cal stems, furnished with hairs, or barbed filaments ; the an- 

 terior pair, representing the second jaws, differs a little from 

 the following ones : it is compared to sorts of hands by 

 Jurine. Each of the three following segments serves as an 

 attachment to a pair offset, composed like the two last of the 

 preceding. Two of the antennae, superior to the others, are 

 longer, setaceous, simple, and composed of a great number of 

 small articulations ; they facilitate by their action the move- 

 ments of the body, and almost perform the office of feet ; the 

 inferior [antennulce, Jurine) are filiform, present most generally 

 but four articulations, and are sometimes simple, sometimes 

 forked. They make by their rapid movements a whirlpool in" 

 the water. In the males, the upper antennae, or one only, pre- 



