ENTOMOSTRACA. 237 



but in this respect, Straus, as well as M. Jurine, Sen., although pre- 

 ceded by Randohr in the observation of several important details of 

 organization, of Avhose memoir on the Monoculi, 1805, they seem to 

 have been ignorant, has surpassed them all. Fabricius merely 

 adopted the genus Limulus of Miiller, which he placed in his class of 

 the Kleistagnatha, or our family Brachyura of the order Decapoda. 

 All the other Entomostraca are united as by Linnaeus in one single 

 genus, Monoculus, which he places in his class of the Polygonata or 

 our Isopoda. 



These animals are all aquatic and mostly inhabit fresh water. 

 Their feet, tlie number of which varies, and that sometimes extends 

 to beyond a hundred, are usually fitted for natation only, being some- 

 times ramified or divided, and sometimes furnished with pinnulye or 

 formed of lamellae. Their brain is formed of one or two globules. 

 The heart has always the figure of a long vessel. The branchiae 

 composed of hairs or setae, singly or united, in the form of barbs, 

 combs or tufts, constitute a part of those feet or of a certain number 

 of them, and sometimes of the upper mandibles *. Hence the origin 

 of our term Branchiopoda, affixed to these animals, of which at first we 

 formed but a single order. Nearly all of them arc provided with a 

 shell composed of one or two pieces, very thin, and most generally 

 almost membranous and nearly diaplianous, or at least with a large 

 anterior thoracic segment, frequently confounded with the head, which 

 appears to replace the shell. The teguments are usually rather 

 horny than calcareous, thereby approximating these animals to the 

 Insecta and Arachnides. In those which are provided with ordinary 

 jaws, the inferior or exterior are always exposed, all the foot-jaws 

 performing the office of feet properly so called, and none of them 

 being laid upon the mouth. The second jaws, those of the Phyllopa 

 at most excepted, resemble these latter organs ; Jurine sometimes 

 distinguishes them by the name of hands. 



These characters distinguish the gnawing Entomostraca from the 

 Malacostraca ; the others, those which constitute our oKler of the 

 Poecilopoda, cannot be confounded with the Malacostraca, inasmuch 

 as they are deprived of organs of mastication, or because the parts 

 which seem to act as jaws are not united anteriorly nor preceded by 

 a labrum as in the antecedent Crustacea and the gnawing Insecta, 

 but are simply formed by the branches of the locomotive organs, 

 which, for that purpose, are furnished with small spines. The Poe- 

 cilopoda in this class of animals represent those which in that of 

 insects are known by the name of Suctoria or the Suckers. Nearly 



* See Ci/pris, 



