116 REJECTED SHELLS OF CRABS. 



sheaths, the claws with the hair attached, even the 

 gastric teeth, all remain with wonderful exactness. 



To look at the rejected shell, indeed, any person 

 not previously acquainted with the fact would 

 naturally suppose that he saw before him the living 

 animal, a close inspection being necessary to dispel 

 the illusion. As soon as the crab has emerged from 

 its old covering, it increases with such astounding 

 rapidity, that at the end of one or two days it can 

 grow no larger until the next moulting time. 



In referring to my own introduction to the subject 

 of exuviation, I may be allowed to notice the an- 

 noyance a young aquarian experiences from the 

 rapidity with which the tank water is apt to become 

 opaque. As such a state involves considerable 

 trouble, especially when the occupants of the tank 

 are the subjects of continued observation, I may 

 mention, in passing, that the means I adopted to 

 correct this state of matters was either to syringe 

 the water frequently, or what seemed to answer still 

 better, to permit it to run off by a syphon into a 

 basin on the floor. 



When the opacity of the tank is occasioned by 

 decaying animal matter, the only temedy is to re- 

 move the offending 'remains/ But with many of 

 the common inhabitants of the tank the crustaceans, 

 for example great difficulty is often experi- 

 enced in ascertaining their state of health, with a 

 view to sanitary investigation. As these creatures, 



