312 History of British Entomostram. 
is usually much the largest of all, we find the eye, the antennae, 
mandibles, mouth, one pair of organs which J urine calls hands, and 
one pair of feet. The eye is situated near the upper extremity of 
this first segment, and in the centre. It is generally pretty large, 
and is single. In C. Castor we can perceive the muscles which 
move it, and which are pretty numerous ; the eye itself is of a 
beautiful ruby colour. The antennae are four in number. The su- 
perior antennae arise from the upper portion of the segment, on each 
side of the eye ; they are always larger than the inferior pair, and 
are generally composed of numerous articulations, which are plenti- 
fully supplied with short setae ; the number of articulations differ in 
each species. The male is distinguished by a peculiarity in the an- 
tennae, which at once marks the sex. In general they are shorter 
and thicker than in the female, and either one, the right one, as in 
C. Castor, or both, as in C. quadricornis, &c. have a swelling near 
the centre, or towards the extremity, followed by a moveable joint, 
which acts like a hinge, and which serves a very useful purpose in 
the act of copulation. The inferior antennae, or antennules, are si- 
tuated immediately beneath the preceding, and are composed of few- 
er articulations. Both of these organs are made use of by the ani- 
mal to assist itself in progressive motion. Immediately below the 
antennules are the internal mandibles, which may be described as 
consisting of three parts, body, neck,* and " barbillon," but differ- 
ing from each other in several respects in the different species. In 
the C.quadricornis are two organs, partly covering these, which Jur- 
ine calls external mandibles, t and which do not exist intheother spe- 
cies ; and in the C. Castor and minutus again, are to be seen two 
round bodies which open and shut during the time the animal is tak- 
ing food, and which do not exist in the quadricornis ; these Jurine 
calls lips. The action of the internal mandibles is to reduce the ob- 
jects of food when large into small pieces, fitted to pass by these lips 
into the mouth. Below the mandibles are situate two organs, which 
Jurine calls hands ; a term which Muller had already applied to the 
same organs in one marine species he describes, the C. ckelifer. J 
All the species of the genus possess these organs, They are always 
situated in the same place ; but all differ from each other in so many 
respects, that it will be necessary to describe them in each species 
separately. The use of these organs, according to the author I have 
already quoted so often, is to push constantly towards the mouth a 
* Prolongation of Jurine. 
j- " Machoires." Latreille. 
J " Entomostraca." P. 114, 
