238 
CRUSTACEA. 
all of them are pai’asitical, and they seem to lead to the Lernsese by 
insensible gradations ; but the presence of eyes, the faculty of 
changing their skin, or even of undergoing a sort of metamorphosis*, 
and that of locomotion by means of their feet, appear to us to esta- 
blish a positve line of demarcation between the former and the latter 
We have consulted several erudite naturalists with respect to these 
transformations, but none of them have observed a change of skin to 
occur. The antennae of the Entomostraca, whose form and number 
greatly vary, serve for natation in several. The eyes are rarely placed 
on a pedicle, and when this is the case, that pedicle is a mere lateral 
prolongation of the head, and is never articulated at the base ; they are 
frequently closely approximated and even form but one. The organs 
of generation are situated at the orgin of the tail ; it has been thought 
but erronenously, that their seat was in the antennae of the male. This 
tail f is never terminated by a fan-like fin, nor does it present those 
false feet observed in the Malacostraca. The ova are collected under 
the back, or are external, and covered by a common envelope, and 
resemble one or two small clusters at the base of the tail ; it appears 
that they can be kept in a desiccated state for a long period without 
losing their properties. 
It is only after a third change of skin that these animals become 
adult and capable of continuing their species. It has been proved, 
with respect to some of them, that a single copulation fecundifies 
several successive generations’ 
ORDER I. 
BRANCHIOPODA. 
A mouth composed of a labrum, tAvo mandibles, a llgula, and one 
or two pairs of jaws, and branchiae, the first of which, Avhen there 
are several are always anterior, characteriz, this order or the sixth 
of the class. 
These Crustacea are always wandering and are generally protected 
by a shell resmbling that of a bivalve, and furnished with four or tAVO 
* The young of Daphnia, ami of some neighbouring subgenera, and probably also 
those of Cypris and Cytherea, with the exception of size, scarcely differ, if at all, 
from their parents on quitting the egg ; but those of Cyclops, the Phyllopa, and the 
Arguli, experience considerable changes while young, either as respects the form of 
the body or the number of feet. These organs in some, the Arguli for instance, expe- 
rience changes which modify their uses. 
t If A\’e e.xcepted the Phyllopa, the last feet are thoracic, or foot.jaAVS (Ci/pris). 
