62 THE CRUSTACEA 



as the epipodite. In the other families the appendage is more leg- 

 like. The " branchial plate " is commonly present, and sometimes 

 an unsegmented appendage which is regarded as the exopodite. 

 In many Cyprididae the limb forms, in the male, a strong clasp- 

 ing organ (Fig. 36, C), which may be unsymmetrically developed 

 on the two sides. In Cytherella it has, in the male, much the 

 same structure as in the Cyprididae, while in the female it is 

 entirely absent. Finally, in the Bairdiidae and Cytheridae it is 

 quite pediform (Fig. 36, B), with a strong terminal claw, and 

 with or without a branchial plate. 



The completely pediform character of this appendage in many 

 Ostracoda suggests a doubt as to its homology with the maxilla of 

 other Crustacea. This doubt is further strengthened by Miiller's 

 statement that the limb appears to belong to the thoracic rather 

 than to the cephalic division of the body. More important still is 

 the fact that in the course of development a pause in the successive 

 appearance of the limbs occurs before this limb is added to the 

 series. On these grounds there seems to be considerable proba- 

 bility in Miiller's view that the maxilla has been entirely lost in 

 the Ostracoda and 'that the appendage which occupies its place is to 

 be regarded as homologous with the first thoracic appendage of 

 other Crustacea. 



In most Myodocopa the fourth post-oral limb is a maxilliform 

 lobed plate, distinctly segmented only in Cypridina (Fig. 37, A). 

 In Sarsiella and Asterope it is laminar and not lobed. In the 

 Polycopidae it is absent. In the other families it is more or less 

 leg-like (Fig. 37, B), with or without a branchial plate. In some 

 Cytherellidae it forms a clasping organ in the male, while in the 

 female it is reduced to the branchial plate. 



In the Cytheridae, Bairdiidae, and Darwinulidae the fifth post-oral 

 limb is pediform, with a strong terminal claw, and is used for 

 creeping. In the Cyprididae (Fig. 37, D) it appears less adapted 

 for locomotion, and is probably chiefly used as a " cleaning foot " 

 for cleaning the other appendages and the inside of the shell. 

 This is its only function in the Myodocopa (except Halocypridae), 

 where it has a remarkable structure, being long and cirriform, 

 divided into numerous segments moved by two muscles running 

 along its whole length (Fig. 37, C). It is set high up on the side 

 of the body, and the terminal part is armed with setae and 

 chitinous teeth. In the Halocypridae the limb is greatly reduced 

 and in the Cladocopa it is altogether absent. 



A peculiar brush-like appendage found on the side of the body 

 in the males of some Ostracods has been regarded as a vestigial 

 sixth post-oral limb. It is found in a few Cyprididae and in Cytherella 

 behind the last leg, and its position near the first leg (third post-oral) 

 in the Bairdiidae and Cytheridae is explained as the result of a 



