History of British Entomostraca. 313 
current of water, carrying along with it the particles destined for 
the insect's food. Immediately beneath the hands are situated the 
first pair of feet. They are double, consisting of two stalks arising 
from a common base, each stalk consisting generally of from two to 
four articulations, more or less furnished with setae, but varying 
very much in different species, especially the marine ones. Attach- 
ed to the next three segments of the body, and arising from the in- 
terstices between each, we find three other pairs of double feet, in 
general resembling each other exactly. These feet act as true fins, 
and as they are not at all used by the insect for walking, the term 
feet is not so correct as that ofjins. In the tail we find placed the 
organs of generation and their appendages. In the first segment, 
we observe in the female two organs, which differ in appearance in 
each species, and which, as their use is to give support to the ovi- 
ducts which furnish the envelope of the external ovaries, are called 
by Jurine, " les supports, ou fulcra." At the junction of the second 
ring with the third in the same sex, in the C. quadricornis, is situ- 
ate the vulva ; this opening forms also the mouth of the canalis de- 
ferens, which communicates directly with the internal ovary, and 
gives passage to the eggs. In the male of this species, we find the 
genital organs situated also in the second segment of the tail, con- 
sisting of an oval body or papilla, which gives origin to a prolonga- 
tion of three short segments. In most of the other species the male 
organs appear to be situated in the corresponding segment to that 
in the female, which carries the " fulcra," or " supports," The ex- 
ternal ovary, or bag of eggs, springs from where the second segment 
articulates with the third, and is attached to it by a very slen- 
der pedicle. The internal ovaries consist of an opaque mass of solid- 
looking matter, composed of numerous round globules of a dark brown 
colour, disposed round the alimentary canal, and occupying a consi- 
derable space of the interior of the body. This, as I have already 
stated, has a direct communication with the opening at the junction 
of the second with the third segment of the tail, the canalis deferensof 
Jurine; and it is through this canal that the eggs pass into the external 
ovary. The alimentary canal is very perceptible, beginning behind 
at the place which I have mentioned as the situation of the lips, 
and terminating at the extremity of the tail. In the C. Castor the 
heart is very distinctly to be seen under the second and third segment 
of the body. It is oval, and gives origin to two vessels of equal 
size, ene going to the head, and the other to the tail, and has another 
organ attached to it, which Jurine considers the auricle. The pul- 
sations of the heart are very frequent, from 112 to 120 in the minute. 
