Exuviation in the Crustacea. 315 



This is most favourably illustrated by the history of the 

 crustacean tribes. 



While occupied with the Cancer Mcenas, the Shore or 

 Harbour Crab, a dingy brown specimen, A, of medium size, 

 with one limb white, was put outside the window on a sum- 

 mer evening, in a capacious glass vessel of sea-water. In the 

 morning a form exactly resembling its own, only somewhat 

 larger, lay in the vessel. This was a new shell, exuviation 

 having taken place in the night. The resemblance was com- 

 plete ; every organ, even the white limb, was seen in both. 

 The natural colour of this species is green, or it is often 

 variegated green and white, and is sometimes reddish. 



Another specimen, B, was caught of smaller size, the op- 

 posite extremities of the limbs being only thirteen lines 

 asunder, its colour green, with three white patches on the 

 back. In the course of little more than a year five exuviations 

 took place at irregular intervals, the new shell and animal 

 being successively larger on each. The third shell came in 

 uniformly green, the white being entirely obliterated. The 

 limbs expanded two inches and a half on the fourth exuviation. 



As this subject was a male, a female of about the same 

 size was introduced into its vessel soon after the fifth exuvi- 

 ation, but only after they were gorged with food to avert 

 hostilities. Both gave unequivocal symptoms of satisfaction. 

 Their union followed, the breastplate, or (more properly) the 

 apron of each being folded back. This female underwent 

 several exuviations. Its shell was originally of a beautiful 

 intermixture of green and white. On the first exuviation the 

 new shell appeared in perfect purity, with precisely the same 

 colours distributed in the same manner. This shell subsisted 

 210 days. The male survived but a short time ; nor did the 

 union of the animals prove prolific. 



Numerous other examples were afforded by the Cancer 

 Mcenas all to the same purport. The observer must feed the 

 subject of experiment frequently, that is, every day or every 

 second day, and renew the sea water as often. Nothing 

 prognosticates exuviation unless abstinence for one or more 

 days previously, and greater quiescence. The colours are 

 alike vivid on exuviation, as if the animal were at large ; but 



