POLYPHEMUS. 



113 



The intestine is curved, but not convoluted. 



The body of the animal is only partially inclosed 

 within the shell. It is fleshy, and after descending in it 

 about two thirds of its length, turns upon itself from be- 

 hind forwards, and folds itself suddenly backwards, to 

 form a long and slender tail, which projects from the shell, 

 and protrudes externally, extending fully the length of the 

 carapace. It is serrated on the outer edge, and terminates 

 in two long setae. This organ differs very much from that 

 of the Daphnia3, and, as J urine says, seems to serve as a 

 rudder. 



The heart is situated at the same part of the body as 

 in the Daphnise, near the junction of the head and body. 



The lower part of the shell seems to be the matrix or 

 receptacle for containing the ova, which are generally 

 about six in number. 



The legs (t. XVII, f. 1 b] are four pairs, always pro- 

 jecting from the shell externally. They are four-jointed, 

 and provided at the extremity of the last joint with 

 several plumose setae. The fourth pair are shorter than 

 the others, and want these setae. These organs resemble 

 more the legs of the Ci/dojrid<% than the other animals of 

 this family, and are, in accordance with their structure, 

 used by the Polyphemus for swimming. It always swims 

 upon its back, and generally horizontally, with quick re- 

 peated motions of the antennae and legs, which carry it 

 rapidly through the water. 



Like the Daphniae, the Polyphemus has, at particular 

 seasons, the ephippiimi, or saddle, which serves exactly 

 the same purpose as in them. The number of young is 

 not so great as in the Daphnias, seldom reaching, at the 

 most, to the number of ten, but more frequently about six. 

 It is very difficult to make accurate observations on the 

 manners and habits of living and propagating their species 

 in this genus, as the little animals are very difficult to be 

 kept in captivity. In the young, even when in the matrix, 

 it is particularly observable, that the eye very soon makes 



8 



