LETTER VIII. 



ON THE LOCOMOTION OF THE MOLLUSCA. 



THE great importance which, in the preceding arrange- 

 ment, is attached to the locomotive organs, naturally draws 

 our attention to these in the first place ; and we shall find 

 that their various modifications have induced a corresponding 

 variety in the mode in which this class of beings move them- 

 selves. Hence, by throwing a cursory glance among them, 



Fig. 18. 



we might indulge ourselves with what some naturalists de- 

 light in a scene rising by a gradual concatenated series from 

 the half zoophytical mollusk, whose fixidity is permanent as 

 the rock on which it is placed, to the fish-like Cephalopod 

 wandering at freedom through the ocean ; passing from the 

 oyster to the Ligula waving to and fro on a flexile stalk, 

 thence to the burrowing bivalves, which gradually lessen in 

 dependency on their furrows and mingle with their halting 

 congeners ; among whose tribes, again, there are some that 

 floating on the surface lead us to the Gasteropods, which, 

 through many a linked transition, pass insensibly to the 

 winged natatory Pteropods. There are, in this hasty sketch, 

 many chasms which a little ingenuity might fill up with 

 osculant groups, and connect the horrid gaps which the 

 naturalists alluded to seem to abhor as much as Nature her- 

 self is said to abhor a vacuum ; but the scene would then be 



