THE OSTRACODA 



61 



The structure of the maxillula varies very much in the different 

 genera. The most primitive form is probably that found in the 

 Cladocopa, where it consists of a protopodite of two segments, a 

 three-segmented endopodite, and a small exopodite of one or two 

 segments (Fig. 35, E). The segments of the protopodite are 

 each produced inwards into a slight masticatory lobe. In the 

 Halocypridae and most Cypridinidae (Fig. 35, D) the structure 

 is similar, save that the exopodite is wanting. In most Podocopa 

 the masticatory lobes are greatly produced, and the distal one is 



Fio. 36. 



A, third post-oral appendage (so-called " second maxilla ") of Cwridinamediterranea(yo\\n). 

 B, third post-oral appendage (so-called "first leg") of Cythereis contract. C, third post-oral 

 api>endage (so-called " maxilliped ") of Macrocypris succinea, male. D, the same, female. (After 

 G. W. Muller.) i, endopodite ; ex, exopodite. 



divided into two. The three segments of the endopodite may be 

 distinct or may fuse into one. A large " branchial appendage," with 

 radiating setae, may perhaps represent the exopodite (Fig. 35, F). 



The third post-oral limb is of very diverse form, and has received 

 different names in the various genera. Thus in the Cypridinidae 

 it has been called the " second maxilla," in the Halocypridae and 

 Cyprididae the "maxilliped," and in the Cytheridae and other 

 families the "first leg." In the Cypridinidae it is quite maxilli- 

 forin, and in the adult shows hardly any trace of segmentation. 

 In young stages, however, Muller finds that it consists of six 

 more or less distinct segments, of which two are assigned to the 

 protopodite and the remainder to the endopodite (Fig. 36, A). 

 A " branchial appendage " is present and is probably to be regarded 



