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 setae, 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 of feet, 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- 
