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SUPPLEMENT 
membranaceous parts ; 3d. a third stratum, still thicker, of a 
less compact texture, in which the calcareous molecules are 
deposited, which give solidity to the testa; 4tli. a last stratum, 
altogether external, composed of colouring matter, or pigmen- 
tum, and an epidermic layer. 
The name of moulting has been given to the renovation of 
the testa in Crustacea. These moultings are more or less fre- 
quent according to the age of the animals, and the more or 
less rapid degrees in which their growth is developed. 
In the decapod Crustacea, the moulting takes place every 
year, towards the middle of the spring. Reaumur has studied 
that of the river crawfish, or astaci, and to him we are in- 
debted for every thing we know concerning the mode in 
which this operation takes place. When these Crustacea are 
desirous of changing skin, they rub their feet one against the 
other, and put themselves into very considerable motion. 
They afterwards swell out their body in a very sensible degree, 
and the first segment of the tail appears more separated than 
usual from the posterior edge of the carapace. The membiane 
which unites them breaks, and the body, with its new skin, 
appears. After a short term of repose, they begin to agitate 
themselves afresh, inflate and raise themselves more than they 
did at first ; the carapace rises, is detached, and remains ad- 
herent in no place except towards tlie mouth. Soon aftei, the 
eyes are disengaged from their old skin, which remains fixed 
to the former testa, then the antennae, as well as the parts of 
the mouth, and finally the carapace, are almost totally sepa- 
rated. At last, after divers reiterated movements, the astaci 
strip their claws and feet in an indeterminate order. Then 
they quit their carapace altogether, and suddenly extending 
their tail, they disengage themselves entirely from their old 
envelope. 
After the moulting, the astaci are very soft, and remain in a 
