ENTOMOSTRACA. 
237 
hut 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 whose memoir on the Monoculi, 1805, they seem to 
have been ignorant, has surpassed them all. Fabricius merely 
adopted the genus Limulus of Muller, 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 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, are usually fitted for natation only, being some- 
times ramified or divided, and sometimes furnished with pinnulae or 
formed of lamellae. Tlieir brain is formed of one or two globules. 
'J’he 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 Imt 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 diaphanous, or at least with a large 
anterior thoracic segment, frequently confounded with the ]iead,whicli 
appears to replace the shell. The teguments are usually rather 
horny than calcareous, thereby approximating these animals to the 
Insecta and Arachnidcs. In tliose 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 
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. Neaidy 
* See Cypris, 
