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 

 onrani/ation, of wljose memoir on the Monoculi, 1805, they seem to 

 have been ignorant, has surpassed them all. Fabricius merely 

 a<loj>trd the genus Limulus of Miiller, which he placed in his class of 

 tin- 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 Tsopoda. 



These animals are all aquatic and mostly inhabit fresh water. 

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

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

 times r;'iui!ied or divided, and sometimes furnished with pinnulae 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 are provided with a 

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

 almost membranous and nearly diaphanous, 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 

 ln>eota 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 order of the 

 Pcecilopoda, 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 witli small spines. The Pce- 

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

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



