CRUSTACEA. 
434 
holes in walls, under stones, &c. They feed upon decaying vegetable and animal matter, and only come forth I 
from their retreat in wet and moist weather. They crawl but slowly, at least, when not alarmed. The eggs are | 
inclosed in a pectoral pouch. Tire young, when first hatched, are destitute of one of the thoracic 'i 
segments, and consequently of a pair of legs, which they subsequently acquire. They were formerly ^ 
much used in medicine, but their employment has long been discontinued. (Types, Oniscus mu- 
Fab. ; Cloporte ordinaire, Cloporte aselle,J)e Geer.) 
Porcellio, Latr., differs from Oniscus in having only seven joints in the lateral antennae. {Oniscus 
asellus, Cuv.) 
Armadillo, Latr., differs from all the preceding in the posterior appendages of the body not being 
exserted. The last segment is triangular. The lateral antennae have only seven joints, the upper sub- 
abdominal plates have a row of small apertures. {Oniscus armadillo, Linn. ; O. cinereus, Panzer — 
Armadillo pustulatus, Armadillo officinalis, Dumeril, from Italy, a species formerly much 
employed by the apothecaries.) ! 
SECOND GENERAL DIVISION. y 
CRUSTACEA ENTOMOSTRACA (Muller). 
Under this denomination, formed from the Greek, and signifying insects in a shell, 
Otho Frederick Muller comprised the genus Monoculus of Linnteus, to which some of 
his Lerntese must also be added. The researches of Muller upon these animals, of ii 
which the investigation is rendered the more difficult owing to their general micro- | 
scopical size, together with those of Schaffer and the elder Jurine, have excited the 
admiration, and merit the thanks, of all naturalists. Other works, but of a more par- ii 
tial nature, as those of Ramdohr, Strauss, the younger Hermann, the younger Jurine, | 
Adolphe Brongniart, Victor Audouin, and Milne Edwards, [to which we may add the ! 
more recent memoirs of Dr. Loven in Sweden, of Dr. Johnston and William Baird in ■[ 
our own country, and of Dana in America] , have greatly extended our acquaintance | 
with these animals, especially in respect to their anatomy. M. Strauss far surpasses |i 
the others, although forestalled, as well as the elder Jurine, in various important struc- I 
tural observations, by Ramdohr, whose memoir upon Monoculus, published in 1805, | 
appears to have been unknown to those authors. Fabricius contents himself with* 
adopting the genus Limulus of Muller, which he places in his class Kleistagnatha, or * 
our Brachyurous Decapo da. All the rest of the Entomostraca he reunites, after* 
Linnaeus, in a single genus Monoculus, placed in his class Polygonata, or our Isopo-iis 
dous Edriopthalma. ■ 
All these animals are aquatic, and ordinarily inhabit fresh water. Their legs, of 
which the number is variable — reaching, in some species, to beyond a hundred — are 
generally fitted only for swimming, and are sometimes ramified or divided, sometimes * 
ornamented with long feathered hairs, or composed of plate-like joints. Their nervous* 
system is composed of only one or two globules. The heart has also the form of aj' 
long vessel. Their branchiae, composed of hairs or threads, either isolated or united,|| 
so as to form beards, combs, or tufts, form part of the legs, or at least of a certain® 
number of them, as well as, occasionally, of the mandibles and upper maxillae. (See J 
Cypris.) Hence the origin of the name Branchiopoda, which we applied to these ani- | 
mals, and which we at first united into a single order. J 
Nearly all the species have a shell of one or two pieces, of very slender consistence,'^*' 
and generally nearly membranous and almost diaphanous, or at least they have a large 
anterior thoracic segment, often soldered with the head, and appearing to occupy the « 
Fig. 15.- 
Armadillo 
pustulatus. 
