ENTOMOSTRACA. 435 



situation of the sliell. Tlie teguments of tlie body are ordinarily corneous rather than 

 calcareous, iu which respect these animals approach the Insecta and Arachnida. In 

 those which are furnished with ordinary maxilla% the inferior or exterior are always 

 naked ; all the foot-jaws performing the office of legs, projjerly so called, none of them 

 being apphed to the mouth. The second maxilhr, 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 sen'e as maxilla; 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 coxk of the locomotive organs, which are 

 armed for this purpose with small spines. The Pcecilopoda 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 

 Lern;eaE ; 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 establfsh a positive line of de- 

 marcation between these animals and the parasitic Lernrea;. We have consulted, in 

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

 served the Lern£ea3, and none of them have ever observed the change of skin. 



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

 and in some species are employed as organs for 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 

 ])laced close together, and sometimes even become confluent, so as to exhibit but one 

 e3'e. 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 seen to exist in the Malacostraca. The eggs are arranged 

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

 velope, having the appearance of one or two minute burrches 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 obsen'ed, in 

 respect of some of them, that 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 LatreiUe, 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 

 ditFercnt classifications have been proposed. The following is of course that of the 



' 'I'hc -ouziu' of llic Dapliiiia*, nnd of some allieJ suligeiii-ra, such, 

 cs|icciiill)', as Cypris and Cythere. do not rtilTor, or liuL very slightly^ 

 from tlieir pnreats in ottier respects tloin tlott of size, even at llie 

 pi riod of bursting frfoii tliC cgijs. Tliose, iiowcver, of Cyclops, ttic 

 I'liyliopoda, and Ari,'ulus, are subject, in tfieir earlier life, to evident 



lianges, either in the form of the hody or the number of leps. These 

 irtjans also undergo changes iu some species wliich entirely alter 

 heir uses. 



t With the exception of the Phyllopoda, the posterior legs are tho- 

 ■acie, or are foot-jans. (Cyprls.) 



F F 2 



