162 CRUSTACEANS. 



after the change takes place, I have never witnessed any return to the 

 original colours. 



The specimen, Plate XXXIV. fig. 5, had a white limb ; I kept it 

 carefully to discover what would ensue on exuviation, for theory here 

 was useless. The animal cast its shell, and the same limb came in white 

 a.s before. 



This fact is very perplexing, whence is the colour derived ? It 

 would be a strong argument for maintaining that the new shell is gene- 

 rated in the old, as within a sheath. Therefore we must not lose sight 

 of it, 



Reproduction of defective parts. The Cancer manas being so com- 

 mon, so easily obtained and preserved, it is peculiarly adapted for the 

 investigations of the inquisitive into the various processes operated by 

 the energies of Nature. 



Herein, I believe, many vulgar errors may be corrected ; some ori- 

 ginating in fallacious principles ; others from precipitate conclusions, 

 inherited from the days of ignorance. 



It is commonly admitted, that new limbs are produced to replace 

 those whereof such Crustaceans, as the species under consideration, have 

 been wholly or partially deprived by violence ; that regeneration exactly 

 compensates privation ; and that, whether a leg or a claw be torn off, 

 another will be generated from the vacant stump of the member. 



No doubt the general principle is true. But Nature's modus ope- 

 rand i, the circumstances and the precise process of repairing the defect, 

 do not correspond with the vulgar sentiments, which are alike unfounded, 

 in ascribing the loss of the Lobster's claws to thunder. 



Such errors probably arise from the casual inequality appearing 

 among the different members of various species of the Cancer, and in 

 failing to discriminate those species of the Astacus, wherein there is a 

 natural disparity in the size of the claws ab originc. 



Perhaps it might be better to amalgamate all that can be said on 

 the subject with subsequent discussion, were it not that naturalists, oc- 

 cupied by special pursuits, commonly desire special illustrations of their 

 special subjects. 



