CRUSTACEA. 293 



accomplished without long continued efforts. 

 Sometimes the legs are lacerated or torn off, in 

 the attempt to withdraw them from the shell ; 

 and in the younger Crustacea the operation is not 

 unfrequently fatal. Even when successfully ac- 

 complished it leaves the animal in a most lan- 

 guid state : the limbs, being soft and pliant, are 

 scarcely able to drag the body along. They are 

 not, however, left altogether without defence. 

 For some time before the old shell was cast off, 

 preparations had been making for forming a new 

 one. The membrane which lined the shell had 

 been acquiring greater density, and had already 

 collected a quantity of liquid materials proper 

 for the consolidation of the new shell. These 

 materials are mixed with a large proportion of 

 colouring matter, of a bright scarlet hue, giving 

 it the appearance of red blood, though it differs 

 totally from blood in all its other properties. As 

 soon as the shell is cast off, this membrane, by 

 the pressure from within, is suddenly expanded, 

 and by the rapid growth of the soft parts, soon 

 acquires a much larger size than the former shell. 

 Then the process of hardening the calcareous in- 

 gredient commences, and is rapidly completed ; 

 while an abundant supply of fresh matter is 

 added to increase the strength of the solid walls 

 which are thus constructing for the support of 

 the animal. Reaumur estimates that the lobster 

 gains, during each change of its covering, an 



