CLASS X. 
CRUSTACEANS (CRUSTACEA)’. 
THe class of crustaceans is the last of articulate animals with 
articulate feet (see above, p. 248), all of which Linnaus regarded 
as insects. They breathe by means of gills, and there are no air- 
passages or stigmata present as in insects. They are distinguished 
from the preceding class by the presence of abdominal feet. The 
myriapods alone agree with the crustaceans in this respect, and are 
by some writers enumerated amongst them, with which, however, 
on account of the presence of air-passages and air-tubes and of their 
resemblance to insect-larve, they ought not in our opinion to be 
united. 
The name of the class is derived from the nature of their 
external covering ; this is in most cases hard, and contains a greater 
or smaller quantity of carbonate of lime. In other instances, how- 
ever, the integument is more leathery or horny. The tissue which 
supplies a foundation for the hard calcareous shell, is still the same 
chitine which forms the dermal skeleton in the entire division 
of articulate animals with articulate feet (p. 284). The shell 
consists of different layers, with a layer of pigment beneath or 
equably penetrated by colourmg matter. Between the rings 
1 Besides the works of LATREILLE already cited under the insects, p. 247 (Hist. 
nat. des Crust. et des Ins., and Genera Crustaccor. et Insector.) we would mention as 
principal works :— 
J.P. W. Hersst, Versuch einer Naturgeschichte der Krabben und Krebse. 111. Bd., 
m. illum. Kupfertaf. 4to. Berlin u. Stralsund, 1782—1804. 
Suckow, Anatomisch-physiologische Untersuchungen der Insekten und Kriistenthiere. 
Heidelberg, 1818, 4to. 
A. HE. DesmArest, Considérations générales sur la classe des Crustacés. Paris, 
1825, 8vo. avec 56 pl. In this work (pp. 396—420) there is a copious list of writings 
on the class of the crustaceans. 
Mitnrt Epwarps, Histowre naturelle des crustacés, ay. pl. Paris, 1834—1840, Il. 
Vols. 8vo. 
Tu. Bui, History of British Crustacea, London, 1853. 
Also the article Crustacea by the same author in Topp’s Cyclopedia 1. pp. 750— 
787 may be consulted. For the fossil species Brocniart et DESMAREST, Hist. nat. 
des Crustacés fossiles sous les rapports zoologiques et géologiques. Paris, 1822, 4to. 
