Shidii's cm riiafiiii' (_)sli'aco(ls 



47 



is taken to be tlie tii'.st cndopoditc joint. The families Cyfridae, Darwinuiidae, Nesideidae, 

 Cytheridae and Cytherellidae: The backward pointing branch is taken as the endopodite, but 

 G. W. MtJLLBR did not feel quite certain about this explanation, cf. below; tliis uncertainty is 

 also expressed in his work of 1912; in the latter work we read on p. 105 ,,der hintere Ast, den 

 ich als Endopodit bezeichne (obwohl die Deutung nirht sicher)" . . .; the forward pointing process 

 is homologized with the exopodite. 



Sixth limb: — Like the following limb this is, as we know, quite absent in the familv 

 Polyeopidae. so that in this case, as in the case of the second antenna, the mandible and the 

 maxilla, this family cannot throw any light on the conditions in the other groups. 



The families Halocypridas, Cypridae. Darwinvlidae, Nesideidae, GytJieridae and Cythe- 

 rellidae: In these families the sixth limb shows such far-reaching agreement with the fifth limb 

 that there seems to me to be no serious reasons against carrying out quite the same homo- 

 logization for both these appendages. In other words there seem to b(> for the sixth limb, as 

 for the fifth one, two quite different explanations possible. According to the first of these two 

 methods of explanation the vibratory plate is to be taken as an epipodial appendage, and 

 the backward pointing rod-shaped branch as the exopodite. The endopodite is scarcely ever 

 developed ; only in the Halocypridae is there often a part (without any endite) that must be 

 homologized with the part that has been explained as the endopodite on the fifth limb; cf. p. 4.3 

 above and fig. 30 of Conchoecia symmetrica G. W. MOLLER, in this treatise below. According 

 to the second method of explanation the vibratory plate is homologous with the exopodite, 

 the backward pointing rod-shaped branch with the endojjodite. The vibratory plate is well 

 developed only in H a 1 o c y p r i d s and C y t h e r e 1 1 i d s; in all the others it is more or 

 less completely reduced. There are no endites. 



It seems to me that it is somewhat more difficult to explain this limb in the C y p r i- 

 d i n i d s. In all the forms of this group it is. as we know, developed as a broad, flattened 

 appendage. In the families Sarsiellidae and Asteropidae it lacks — presumably secondarily — 

 entirely or almost entirely all traces of division into joints and, in other respects as well — 

 this is especially the case in the Sarsiellidae — it is very slightly differentiated. It is, of 

 course, quite impossible to carry out a detailed homologization in these two families. — The 

 family Cypridinidae: In this family the structure of the sixth limb is more complicated; in most 

 cases it has well developed joints; the variation in the structure of this limb is, however, rather 

 slight in this group. According to the first method of explanation the proximal joint of this limb, 

 which is almost always characterized, as shown, for instance, in the accompanying fign?i'. Iiy two 

 bristle-bearing endites on the anterior edge, is presumably to be regarded as a procoxale 

 and a coxale, the following joint, which also has a powerful endite on the anterior edge, 

 appears to correspond to the basale; the two following joints, the proximal one of which 

 is relatively short and is armed on the anterior edge with a powerful endite, while the 

 distal one is comparatively large and has no endite, correspond to the exopodite; the 

 collection of short bristles, which sometimes issues on a lobe-like little process almost always 

 found on the posterior edge of the protopodite, is, according to this method of explanation, 

 to be considered as the remains of an epipodial appendage; cf. the accompanying figure ^ If : I. 



Sixl/i /mill. 



Hiilncypridae. 



( ypridae, Danvin - 



iilidae, Nesideiilne. 



Cfllheridne and 



( 'yllierHlidnp. 



Ciipridinidac 



Snntiellidar find 



.isternpidne. 



