25 1? Mr. Baird on British Eniomostraca. 



digitations or Bpim s. The fourth pair (fig. B.) La very similar 

 to, hut rather Bmaller than, the third, and has only Bixty-five 



branchial filaments. The fifth pair (fig. 9.) differ in many 



respects from the four preceding ones : the first joint [a much 



the same as in tin* other feet, bul the second, or vesicle (a), is 

 kidney-shaped instead of heart-shaped. From this joint, and 

 inferior edge of the first, arises an elongated plate (/>), which 



has no filets. Behind this plate arises also from the second joint 

 another (c), very short and broad, arched upwards, and ter- 

 minating above in a flat, plumose, or rather ciliated prolon- 

 gation. Inferiorly it terminates by a small moveable joint (d) 

 bavin"- a Lone needle directed downwards, without cilia. Ju- 

 rine says this last pair of feet are not inserted into the body 

 of the insect, but the one is confounded with the other on 

 the opposite side ; the junction of the two forming the com- 

 mencement of a gutter or canal, which is prolonged along the 

 immediate attachment of the anterior 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 cur- 

 rent which enters the shell by the anterior part, carrying the 

 molecules, &c. in the water to the posterior part, where the 

 gutter commences, 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 for locomotion. The first 

 and second pairs according to Straus are used by the insect for 

 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 above-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 first pair 

 ceases, but in them, on the contrary, is then accelerated. The 

 grand use of the third and fourth pairs is for respiration, be- 

 ing adapted for that purpose by their branchial plates, which, 

 as DeGeer had already observed, serve the same purpose to 

 these insects as the gills of crabs, certain aquatic insects and 

 larvae, fishes, &c. The second joints of these feet, which I 

 have above described as heart-shaped vesicles, were con- 



