424 CUUSTACEA. 



The abdomen can also be protruded ; it either ends in a caudal fork 

 (Cypris and Cythere), or has the form of a plate armed with spines 

 and hooks on its posterior margin (Cypridina). 



Appendages. The two pairs of antenna? are placed on the 

 anterior region of the body (fig. 336, A', A"), and are used as creep- 

 ing and swimming legs. In Cypridina, however, the anterior pair 

 is provided with olfactory hairs. The antennas of the second pair in 

 Cypris and Cythere resemble legs, and end with strong hooked 

 bristles, by help of which the animal can attach itself to surrounding 

 objects. In the exclusively marine Cypridinidce and Halocypridce 

 this pair of appendages has the form of biramous swimming feet, 

 which consist of a broad triangular basal plate, a many-jointed 

 endopodite beset with long swimming seta 1 , and a rudimentary 

 exopodite, which, however, is stronger in the male and furnished 

 with hooks of a considerable size. 



In the region of the mouth beneath and to the side of a tolerably 

 large upper lip there are two powerful mandibles with a broad and 

 strongly toothed biting edge. The mandibular palps, which are 

 leg-like and elongated, are usually three -jointed and can be used as 

 legs (Mdf). In exceptional cases (Paradoxostoma), the mandibles 

 are styliform and are enclosed in a suctorial proboscis formed from 

 the upper and under lips. 



The mandibles are folloAved by the first pair of maxilla?, which 

 are in all cases distinguished by the great development of their 

 basal portion and by the reduction of the palp. In the Cypridcv 

 and Cytheridce the basal joint of the first maxilla bears a large 

 comb-like setose plate, which by its swinging movements aids the 

 function of respiration, but does not itself function as a gill. A 

 similar branchial plate may also occur on the two following appen- 

 dages (the 5th and 6th pair), which sometimes have the form of 

 jaws, sometimes of legs. The anterior of these appendages (maxilla 

 of the second pair or better maxilliped, fig. 336, MX") functions, in 

 Cypris, chiefly as a jaw, but bears, besides the rudimentary bran- 

 chial appendage, a short, backwardly directed, usually two-jointed 

 palp, which, however, in certain genera and in Halocyprls becomes a 

 short, three-jointed or even four-jointed leg. In Cythere it acts ex- 

 clusively as a leg, and represents the first of the three pairs of legs 

 present in this animal. In the Cypridina, however, it has completely 

 the form of a jaw, and is provided with an enormously developed 

 branchial plate (fig. 336 a, MX"). The appendage of the sixth pair 

 is usually modified to an elongated, many-jointed, creeping and ad- 



