CRUSTACEA. 263 



are mixed with a large proportion of colouring 

 matter, of a bright scarlet hue, giving it the ap- 

 pearance 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 ingredient 

 commences, and is rapidly completed ; while an 

 abundant supply of fresh matter is added to in- 

 crease 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 animal, for the supply of the large quantity 

 of calcareous matter required for the construction 

 of the shell at the proper time. A magazine of 

 carbonate of lime is collected, previous 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 

 disappear. 



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 time replaced by a new claw, 

 which grows from the stump of the one which had 

 been lost. It appears from the investigations of 



