CRUSTACEA. 209 



is not accomplished without long continued cfTorts. Some- 

 times 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 success- 

 fully accom])lished, it leaves the animal in a most languid 

 state: the limbs, being soft and pliant, are scarcely able to 

 drag the body along. They are not, however, left altoge- 

 ther 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 quan- 

 tity of liquid materials proper for the consolidation of the 

 new shell. These materials are mixed with a large propor- 

 tion of colouring matter, of a bright scarlet hue, giving it 

 the appearance of red blood, thougli 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 sud- 

 denly 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 ingredient 

 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 increase of one-fifth of 

 its former dimensions. When the animal has attained its 

 full size, no operation of this kind is required, and the same 

 shell is permanently retained. 



A provision appears to be made, in the interior of the ani- 

 mal, for the supply of the large quantity of calcareous mat- 

 ter required for the construction of the shell at the proper 

 time. A magazine of carbonate of lime is collected, pre- 

 vious to each change of shell, in the form of two rounded 

 masses, one on each side of the stomach. In the crab 

 these balls have received the absurd name of crab's eyes; and 

 during the formation of the shell they disap])car. 



It is well known that when an animal of this class has 

 been deprived of one of the claws, that part is in a short 



Vol. I. 27 



