OBU8TAOBAH8. HI 



>ut)j,-.-t ..i various specie*. But to admit of progressive increment, it i- 

 tnijiK'ntly renovated, and especialK during <-arlierage. While it subsists 

 in pcrftvtion. the subject does not grow, for apparently the only period 

 f increment i- n-.trict.-il to preporntion for its exuviation, or cant i n- 

 i if the internment. Whence the importance ..f this physical alternative 

 i ohvious. The precise period of the commencement and cessation ..t 

 its occurrence are alike unknown. I'ndoubtedly it commences soon. 

 and terminates when the full dimension* are attained ; for, in the lidit 

 that \ve consider its pur]x>se, there i- no further use for the change 



shells of living Crustaceans are of various colours, pven. nil. 



How. When cast, they dry, and the colour fades. The more vivid 

 an- consequently converted to another hue, principally reddish. The 

 same tendency is often exhibited by some still investing the living sub- 

 ject . a No white patches become green on successive exuviations. 



Those young animals which are originally pure white, are darkened 

 by BU|ervening patches ; and possibly the whole integuments are nlti- 



ly converted to the colour usually distiiiiruishinir their sjM-ci.-^. Hut 

 the only Crustacean I have seen white in the early stages, is the ('>u>,;,- 

 vf/v, or Common Cran. 



Many naturalists have viewed the animals, or most of those in- 

 cluded in this section, as nearly akin to insects. Some are terrestrial. 

 others are ac<|iiatic. Only the latter are considered here. 



The shell Ls composed of numerous parts, of which one, the princi- 

 pal, investing the intestinal organs, is called the carapace. Naturalist* 

 ctnujMire the parts of the body to segments, whereof they enumerate 

 twenty-one composing the Common Crab. The parts are connected by 

 a kind of cartilage, which are liberated by its continued maceration, 

 wlu-n their former articulation may be examined in detail. Varim. 

 markable pieces will be then found among them. 



Though composed of so many portions, the whole integument ge- 

 nerally separates entire on exuviation. 



TliLs process is not confined to Crustaceans alone. The integuments 

 of numerous other animals, especially those belonging to the Insect, th. 

 ophidian and Batrachian tribes, are also cast and renovated. But the 



