100 CRUSTACEA. 



or is wider than it is thick. The mouth consists of the same 

 pieces as in the preceding Crustacea; but here, those which 

 correspond to the two superior foot-jaws of the Decapoda, ex- 

 hibit an appearance of a lower lip terminated by two palpi, 

 still more than in the latter. The two mediate antennae are 

 almost obliterated in the last Crustacea of this order, which 

 are all terrestrial and also differ from the others in their re- 

 spiratory apparatus. The male organs of generation are 

 usually announced by linear or filiform appendages, and 

 sometimes by hooks, situated at the internal origin of the first 

 sub-caudal laminae. The females carry their ova under the 

 thorax, either between scales, or in a pouch or membranous 

 sac, which they open in order to allow a passage to their 

 young, which are produced with the form of parts peculiar to 

 theiii species, merely changing their skin as they increase in 

 size. Most of them are aquatic. Those which are terrestrial, 

 like all other Crustacea which live out of water, still require a 

 certain degree of atmospheric humidity to enable them to 

 breathe, and to preserve their branchise in a proper state for 

 the exercise of that function. 



This order according to the system of Linnaeus embraces 

 the genus 



Oniscus, Lin., 



Which we will divide into six sections. 



The first Epicarides, Latr. is composed of parasitical Iso- 

 poda, with neither eyes nor antennae, the body of which, in the male, 

 is very flat, small and oblong; much larger in the female, and having 

 an oval form narrowed and slightly curved posteriorly, hollow be- 

 neath, with a thoracic border divided on each side into five mem- 

 branous lobes. The feet are placed on this border and cannot be 

 used either for locomotion or natation. The under surface of the 

 tail is provided with five pairs of small, ciliated, imbricated leaflets, 

 corresponding to as many segments and arranged in two longitudi- 

 nal series; there is no appendage, however, to the posterior ex- 

 tremity. The only parts distinctly visible in the mouth are two 

 membranous leaflets laid upon another of the same nature, forming 

 a large quadrilateral figure. The inferior concavity, forming a sort 

 of shallow basket, is filled with the ova. Near their outlet is al- 

 ways found the individual presumed to be the male. Its extreme 



