174 CRUSTACEANS. 



production of defective members. Each member is formed entire, there- 

 fore comprehending all subordinate parts. Thus, should a pincer of 

 either claw be defective, it will be generated and produced on exuvia- 

 tion along with the whole claw ; should the hind pair of Umbs be want- 

 ing, they are generated in the dormant subject lying in the old shell, and 

 will be produced as parts of the new subject in the new integument. 

 But no new additions will be generated to restore the sj^inmetry of the 

 original parts. 



The cast shell contains nothing, it is an absolute vacuity. 



Although the integument enclosing the stomach may be possibly 

 derived from some internal coating of the carapace, or some secretion 

 may originate from that source, I do not see how the like can be expected 

 from the old limbs, or, if it could, how it would fuliil a similar office. 

 Neither is it e\'ident that the shell of the limbs is derived from their own 

 contents, though certainly most probable. The new animal is always 

 larger than the old, which rather confirms the opinion maintaining that 

 the original integument is soft and compressible before hardening as a 

 shell. 



I have said much of form, but little of colour, a subject not devoid 

 of interest. The colour of the common crab seems to be always a shade 

 of reddish-brown when in perfection of the adult. That of younger 

 specimens is somewhat variegated, as may be seen of the different figures 

 in the plates. AU are probably advancing progressively to the ordinary 

 colour. I know well that little confidence is to be reposed in colour, 

 and how much it is undervalued by naturalists. Nor am I aware that it 

 ever denotes pecuHar permanent properties. 



It may be affirmed that, until attaining the final hue, the shell is con- 

 tinually undergoing some modification. Thus the specimens, Plate XLI. 

 figs. 5, 6, 7, all of nearly the same size, were delineated mthin a month of 

 each other. The specimen, fig. 5, was originally brownish, very faint. On 

 casting the shell it appeared pure white, with a purplish tinge. Its next 

 exuviation produced a pure white shell, which was followed by another 

 in five or sis weeks, darkening very little until the animal died two or 

 three months later. Tlie specimen, fig. 6, tended first to brownish, then 



