76 m;i iisu KNTOMOSTK.U \. 



differs in many respects from tlic four preceding. It 

 is more rudimentary in form, and can apparently be 

 less readily divided into articulations. The part corre- 

 sponding with the branchial plate is rounded, and has 

 no Jilanieiits springing from its edge. Immediately above 

 it there arises a strong-jointed, plumose spine, which is 

 curved backwards upon this plate, Avhile the third and 

 fourth articulations are represented by finger-like pro- 

 cesses springing from the inferior extremity of the foot, 

 and sending olftwo or three plumose setae. 



Jurine says this last pair of feet are not inserted into 

 the body of the animal, but the one is confounded with 

 the other on the opposite side, the junction of the two 

 forming the commencement of a gutter or canal, which 

 extends along the immediate attachment of the feet to the 

 mouth, where it terminates. These five pairs of feet are 

 in almost constant motion, even when the animal is still 

 and at rest, and their use at such times is to communicate 

 an undulatory motion to the water, from one pair to 

 another; thus establishing a current which enters the 

 shell by the anterior part, carrying the molecules, &c. in 

 the water to the posterior part where the gutter com- 

 mences, and there being driven by the vermicular motion 

 back again to the anterior extremity of the canal or 

 mouth. None of these feet are used lor locomotion. The 

 first and second pairs, according to Straus, are used as 

 organs of prehension. According to Jurine, the chief 

 action of the first pair is to direct the alimentary particles 

 brought up by the current of water, along the canal abo\e 

 described, into the mouth. When the mouth is opened, 

 says the same author, to receive the food, the motion of 

 all the feet, except this lirst pair, ceases, but in them, on 

 the contrary, it is then accelerated. The grand use of 

 the third and fourth pairs is respiration, being adapted 

 for that function by their branchial plates, which, as 

 De Geer had already observed, serve the same purpose 

 to these insects MS the gills of crabs, certain aquatic 

 insects, lar\:e. and fishes. The basal joints of these feet 



