ANNULOSA: CRUSTACEA. 205 



enclosing the entire body. The mouth is not suctorial, but is 

 furnished with organs of mastication. 



This division comprises the two orders Ostracoda and 

 Copepoda. 



ORDER I. OSTRACODA. Small Crustaceans having the entire 

 body enclosed in a shell or carapace, which is composed of two 

 valves united along the back by a membrane. The branchiae 

 are attached to the posterior jaws, and there are only two or 

 three pairs of feet, which subserve locomotion, but are not 

 adapted for swimming. 



The order includes the Cyprides (fig. 63, a), which are of 

 almost universal occurrence .in fresh water. The common 

 Cypris is completely protected from its enemies by a bivalve 

 carapace, which it can open and shut at will, and out of which 

 it can protrude its feet. Locomotion is mainly effected by 

 means of a pair of caudal appendages. The Cypris is ex- 

 tremely prolific, and a single impregnation appears to last the 

 female for its entire lifetime. It appears, also, that the young 

 females, produced in this way, are capable for some generations 

 of producing fresh individuals without the influence of a male 

 (parthenogenesis). 



Fig. 63. Fresh-water Entomostraca. a Cypris tris-striat* ; b Daphnia 

 pulex; c Cyclops quadricomis. 



ORDER II. COPEPODA. Small Crustaceans, having the head 

 and thorax covered by a carapace, and furnished with five 

 pairs of natatory feet. Usually there are two caudal locomo- 

 tive appendages. 



In the Cyclops (fig. 63, c) which is one of the commonest of 

 the "Water-fleas," the cephalothorax is protected superiorly by 

 a carapace, and the abdominal somites are conspicuous. In 

 front of the head is situated a single large eye, behind which 

 are the great antennae and the antennules. The feet are five 



