CHAPTER II. 



Class I. CRUSTACEA. 



THE animals composing this class are distinguished by 

 having the head generally confounded with the thorax, and 

 respiring by branchiae or gills placed at the sides of the body, 

 beneath the hard covering or shell in which they are in- 

 cased. The large and better known species arr those marine 

 animals known under the ordinary name of shell-fish, and 

 in the Linnaean system they composed two genera alone in 

 the apterous order of insects, namely, Cancer and Monncii- 

 lus. Brisson, perceiving the impropriety of allowing these 

 animals to remain amongst the true insects, first separated 

 them forming them, together with the Myriapoda and Arach- 

 nida into a class intermediate between fishes anil insects, 

 thus taking the first step towards a natural distribution of 

 the articulated animals. Fabricius and Latreille, by accu- 

 mulating many valuable materials relative to them, assisted 

 greatly towards the same end, but it is to the immortal Cu- 

 vier that we are indebted for the first separation of the Cnw- 

 turi-ii as a class within its strict limits. 



Since this period Lamarck and Leach, as well as Latrcillc. 

 have occupied themselves in an especial manner in endea- 

 vouring to elucidate this class, distributing its contents into 

 various natural groups. Jurinc. Strauss. Sha\\. Savigny. 

 Audonin, and .Milne Kdwards. h:r,c studied with great suc- 

 cess the oral and internal anatnmv of the Crustacea. In our 



