PACKARD. ] HOMOLOGIES OF THE CRUSTACEAN LIMB. 4i3 
ary processes, is apparently not correct. We regard the Phyllopodous 
limb as not differentiated 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 
portion 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, Estheria, Limnadia (Plates 
I, I1I—V), or in the sections of Hstheria (Plate XXIV), Apus (Plate 
XXXII, fig 2), or Thamnocephalus (Plate XIV, fig. 4). This relation is 
also seen in the lobster or cray-fish upon removing the side of the cara- 
pace; the branchiz 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 portions 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 Branchiopoda 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- 
diade and Apodide they 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 branchites, 
but we have adopted Lankester’s term, exites, for these parts. 
The endopodal or locomotive portion of the limb of the Phylopod 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 Apus 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 Apus limb.” 
(Quart. Jour. Micr. Sc., 1881, p. 365.) 
