36 MECHANICAL FUNCTIONS. 



delicately formed instruments called antenna, or feelers. 

 These, in the Lobster are many inches in length, and 

 composed of a great number of rings, articulated to 

 each other in a most beautiful manner, and furnished 

 with minute muscles on the inside, so as to give them 

 motions in all possible directions, at the will of the ani- 

 mal. Some naturalists have supposed that these are 

 not merely the organs of feeling, but that they might 

 also serve for that of hearing, or smelling also. 



As the coverings of the Crustacea are composed of 

 hard unyielding substances, it is obvious that the animal 

 within must be restrained in its growth, unless some 

 means were provided by which it could relieve itself 

 from such confinement, and accordingly, as nature every 

 where provides for the comfort and perpetuity of the 

 lowest, as well as the highest of her works, so in the 

 case before us, the animal has the power of casting off 

 its old covering when it becomes too small, the same be- 

 ing soon after replaced by a new one, of ample dimen- 

 sions. 



The pocess of casting the Shell. These animals cast 

 their shells once a year ; and the manner in which the 

 Lobster, as an example, draws himself out of his old 

 case, his condition afterwards, and the incipient forma- 

 tion of the new shell, has been particularly investigated 

 by the celebrated Reaumur. 



The Lobster, for some time before the process begins, 

 becomes exceedingly restless, undoubtedly from the 

 pain excited by the pressure of its shell, and thus the 

 poor animal is under the necessity of making violent ef- 

 forts to relieve itself. By this means the shell is burst 

 open along the chest, between the insertion of the legs. 

 The claws are the first parts withdrawn from their 

 sheaths, and next the feet, both of which seem to require 

 much muscular exertion ; the head next throws off its 

 case, together with the many jointed antennae, and the 

 two eyes are disengaged from their horny pedicels. In 

 this operation, not only the complex apparatus of the 



What provision has nature made for the growth of the Crustacea ? In 

 what manner does the lobster cast off its crusty covering? 



