76 
BRITISH ENTOMOSTRACA. 
differs in many respects from the 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 filaments springing from its edge. Immediately above 
it there arises a strong- jointed, plumose spine, which is 
curved backwards upon this plate, while the third and 
fourth articulations are represented by finger-like pro- 
cesses springing from the inferior extremity of the foot, 
and sending off two 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 for 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 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, 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 as the gills of crabs, certain aquatic 
insects, larvae, and fishes. The basal joints of these feet 
