ENTOMOSTRACA. 
435 
situation of the shell. The teguments of the body are ordinarily corneous rather than 
calcareous, in which respect these animals approach the Insecta and Ai;achnida. In 
those which are furnished with ordinary maxillae, the inferior or exterior are always 
naked ; all the foot-jaws performing the office of legs, properly so called, none of them 
being applied to the mouth. The second maxillae, except in the Phyllopoda, also re- 
semble these last-named organs. By Jurine, they are sometimes called hands. 
These characters distinguish the masticating Entomostraca from the Malacostraca, 
The other Entomostraca, or those which compose our order Poecilopoda, cannot be 
confounded with the Malacostraca, being destitute of organs fitted for mastication, or 
because the organs which appear to serve as maxillae are not inserted close together 
anteriorly, and preceded by an upper lip, as in the preceding Crustacea and the man- 
dibulated insects, but merely formed by the coxae of the locomotive organs, which are 
armed for this purpose with small spines. The Poecilopoda represent, in this class, 
those species which, amongst the Insects, are distinguished by the name of Haustellata. 
They are almost exclusively parasitic, and appear to conduct us insensibly to the 
Lernaeae ; but the presence of eyes, the power of changing the skin, or even of under- 
going a kind of metamorphosis*, with the capability of transporting themselves from 
place to place by the help of the legs, appear to us to establish a positive line of de- 
marcation between these animals and the parasitic Lern^^. We have consulted, in 
respect to these transformations, various learned naturalists who have frequently ob- 
served the Lerneese, and none of them have ever observed the change of skin. 
The antennae of the Entomostraca vary, both in form and number, considerably ; 
and in some species are employed as organs for svv^imming. The eyes are very rarely 
fixed upon a footstalk ; and even when this is the case, the peduncle is merely a lateral 
prolongation of the head, and is never articulated at its base. Often the eyes are 
placed close together, and sometimes even become confluent, so as to exhibit but one 
eye. The organs of generation are placed at the base of the tail : it is a mistaken 
notion which has been entertained, that the antennae in some males perform this func- 
tion. The tailf is never terminated by a fan-shaped swimmeret, and is never furnished 
I with the false feet which are seen to exist in the Malacostraca. The eggs are arranged 
I in a mass beneath the back [of the shell] , or are exterior, contained in a common en- 
j velope, having the appearance of one or two minute bunches of grapes, situated at the 
base of the tail. It appears that they are able to remain for a great length of time in a 
! dry state, without losing their properties. It is not until after the third moulting that 
these animals become adult, and capable of reproduction ; and it has been observed, in 
1 respect of some of them, that a single copulation is sufficient to fecundate many suc- 
ij; ceeding generations. 
[By referring to pages 409 and 410, the distributions into orders, &c. of the Ento- 
mostraca, as proposed by Latreille, Milne Edwards, &c., will be perceived to vary 
: somewhat inter se. The question as to the rank of the different groups, subsequently 
, described either as orders or minor divisions, cannot be decided until naturalists are 
agreed as to the relative importance of the organs upon the variations of which these 
different classifications have been proposed. The following is of course that of the 
I * The young of the Daphnise, and of some allied subgenera, such, 
I especially, as Cypris and Cythere, do not differ, or but very slightly 
]j from their parents in other respects than that of size, even at the 
i period of bursting from the eggs. Those, however, of Cyclops, the 
; Phyliopoda, and Argulus, are subject, in their earlier life, to evident 
changes, either in the form of the body or the number of legs. These 
organs also undergo changes in some species ■which entirely alter 
their uses. 
t With the exception of the Phyllopoda, the posterior legs are tho- 
racic, or are foot-jaws. (Cypris.) 
F F 2 
