08 CLASS CONCHIFKRA. 



parated animals that otherwise agreed with each other 

 With respect to the bivalve shells, however, this objec- 

 tion does not hold good, as they all contain animals 

 belonging to the class Conchifera. 



The individuals of this class appear to be deprived of 

 all the senses except that of feeling. Their powers of 

 motion have been so well described by Dr. Roget, in his 

 Bridgewater Treatise, that we cannot do better than 

 extract a portion from that interesting Avork. 



Yalves of the Unio Batava, vith tlie Connecting Ligament. 



The tw^o valves of the shell of the Conchifera are 

 united at the back by a hinge-joint, often very artificially 

 constructed, having teeth that lock into each other ; and 

 the mechanism of this articulation varies much in dif- 

 ferent species. The hinge is secured by a substance of 

 great strength. 



During the life of the animal, the usual and natural 

 state of its shell is, that of being kept open for a little 

 distance, so as to allow of the ingress and egress of the 



