CLASS X. 

 CRUSTACEANS (CRUSTACEA) 1 . 



THE class of crustaceans is the last of articulate animals with 

 articulate feet (see above, p. 248), all of which LINNAEUS 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 arc 

 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-larvae, 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 

 cMtine 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 colouring matter. Between the rings 



1 Besides the works of LATREILLE already cited under the insects, p. 247 (7//V. 

 not. des Crust, et des Ins., and Genera Crustaceor. et Insector.) we would mention as 

 principal works : 



J. P. W. HERBST, Versuch einer Naturgescliichte der Krabben und Krebse. ill. Bd., 

 m. ilium. Kupfertaf. 4to. Berlin u. Stralsund, 178-2 1804. 



SUCKOW, Anatomisch-physiologische Untersuchungen der Insekten und Kriiistenthiere. 

 Heidelberg, 1818, 4to. 



A. E. DESMAREST, Considerations generates sur la classe des Crustaces. Paris, 

 1825, 8vo. avec 56 pi. In this work (pp. 396 420) there is a copious list of writings 

 on the class of the crustaceans. 



MILNE EDWARDS, Histoire naturelle des crustaces, av. pi. Paris, 18341840, in. 

 Vols. 8vo. 



TH. BELL, History of British Crustacea, London, 1853. 



Also the article Crustacea by the same author in TODD'S Cyclopaedia I. pp. 75 

 787 may be consulted. For the fossil species BROGNIART et DESMARKST, ffixl. not. 

 des Crustaces fossilcs sous les rapports zooloyiqu.es et yeoloyiques. Paris, 1822, 4to. 



