PACKARD.] HOMOLOGIES OF THE CEUSTACEAN LIMB. 413 



ary processes, is apparently not correct. We regard the Pliyllopodous 

 limb as not difierentiated into an axially-jointed portion, but that it is 

 divided into a dorsal and ventral portion, the outer side of the limb 

 being epipodal and the inner side endopodal, the endites of Lankester 

 being processes of the endopodal portion. 



Returning now to the general homologies of the Crustacean limb, in 

 the light of Professor Lankester's suggestions as to the nomenclature 

 of the limbs of Apus, and from our knowledge of the limbs of Crustacea 

 from the Copepoda and Ostracoda upward, and more especially the 

 Cladocera, Phyllopoda, and Phyllocarida compared with the Decapoda 

 (the Tetradecapoda being considered as a side branch of the Malacos- 

 traca and not affecting the general homologies here given), we would 

 suggest the following views : 



Looking at the generalized legs of the Cladocera as exemplified in 

 Moina (fig. 28, third pair), we see that there is no specialized axis or 

 stem, and that the limb may be divided into an outer, partly dorsal or 

 respiratory epipodal moiety (the dotted portion in the figures), and an 

 inner, ventral locomotive moiety, which may be called the endopodal 

 X)ortion of the limb. 



Now, if we look at the figures in the plates we shall see that the larger 

 part of the epipodal or respiratory portion of the limb is thrown up over 

 the back, as seen in the side view of Limnetis, Ustheria, Limnadia (Plates 

 I, III-V), or in the sections of Ustheria (Plate XXIY), Apus (Plate 

 XXXII, fig 2), or TJiamnoceplialus (Plate XIV, fig. 4). This relation is 

 also seen in the lobster or cray-fish upon removing the side of the cara- 

 pace; the branchiae and flabellum are thrown up dorsally, while the loco- 

 motive portions of the limb hang down or are usually directed forward. 

 The importance of the epipodal or branchial i^ortions of the limb has been 

 underestimated by writers on the homologies of the Crustacea, because 

 they have viewed the subject from the standpoint of the Decapodous 

 structure, where the epipodites are comparatively unimportant. But in 

 the order Branchiapoda these parts are often quite as well developed as 

 the endopodal, and are not only respiratory, but, as in the large fla- 

 bellum of the Phyllopods, are largely locomotive, while in the Limna- 

 diadce and Apodidm tliey are variously modified to carry the eggs. 



The epipodal portion is differentiated into the flabellum and branchia 

 or gill, the simple gill of the Phyllopods being the homologue of the 

 highly differentiated complex decapod gill ; and the fan-like flabellum 

 of Apus, for example, is the homologue of the scaptognathite of the 

 Decapoda. The gill and flabellum might be properly called hranchites, 

 but we have adopted Lankester's term, exites, for these parts. 



The endopodal or locomotive portion of the limb of the PhyEopod is 

 differentiated into six lobes or endites (Lankester); there being no parts 

 corresponding to the stem or protopodite (the coxopodite and basipodite 

 together) of Decapods. These are to be found only in the Decapoda. 

 In A-pus there is a slight approach to the Decapodous protopodite, but 

 we differ from Huxley or Lankester in regarding the base of the apodid 

 leg as truly axial and jointed, as the supposed joints are shifting and 

 with incomplete articulations. Lankester considers "that the endopo- 

 dite of the Astacus maxillipede is the homologue of the endite 5 of the 

 Apus limb ; its exopodite is homologous with endite 6 of the Apus limb, 

 and its epipodite is homologous with the flabellum of the Aj;«s limb." 

 (Quart. Jour. Micr. Sc, 1881, p. 365.) 



