II. General Division.— ENTOMOSTRACA. 



435 



situation of the shell. The teguments of the body are ordinarily corneous rather than 

 calcareous, in which resjiect these animals approach the Insecta and Arachnida. In 

 those which are furnished with ordinary maxillae, the inferior or exterior are always 

 naked ; all the foot-jaws ijerforming 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 t|ie Mal?costraca, 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, bwt 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 Lernaeae. We have consulted, in 

 respect to these transforapations, various learned naturalists who have frequently ob- 

 served tlie Lernaeae, and none of them have ever observed the change of skin. 



The antennae of the Entomostraca vary, both in form and number, considerably ; 

 flfUd in some species axe eipployed as organs fotr swimming. 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 

 with the false feet which are seep -to exist in the Malacostraca. The eggs are arranged 

 in a mass beneath the baclc [of the shell], or are exterior, contained in a common en- 

 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 

 tiaese animals become ad^ilt, and capable of reproduction ; and it has been observed, in 

 respect of some of them, tiiat a single copulation is sufficient to fecundate many suc- 

 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 



changes, either in the form of the liody or the number of leps. These 

 organs also undergo changes in some species which entirely alter 

 their uses. 



t With the exception of the Phyllopoda, the posterior legs are thv 

 racic, or are foot-jaws. [Cypris. ) 



* The young of the Daphnice, and of some allied subgenera, such, 

 especially, as Cypris and Cythere, do not differ, or but very slightly 

 fmm their parents in other respects than that of size, even at the 

 period of bursting from the eggs. Those, hun-ever, of Cyclops, the 

 Phyliopoda, aud Argulus, are subject, ia their earlier life, to evident 



