Birge—Notes on Cladocera. 
1041 
second foot to the same part While he says nothing further 
in the matter, he seems to have abandoned this view when he 
described Saycia (’04) and it need not be discussed further 
than to say that the first foot of OphryoxUs bears a structure 
which is very plainly the maxillary process (see Lilljeborg), 
and that this structure is as plainly lacking in other Macro- 
thricidae. There is, therefore, no reason to homologize the 
whole of the endopodite with the maxillary process. The ques¬ 
tion of the relation of endopodite and exopodite appears to 
be more difficult and indeed Lilljeborg has plainly varied in 
his interpretation of these parts in different genera. In re¬ 
spect to the third foot there seems to be no difference of judg¬ 
ment. The exopodite of that appendage is so large and dis~ 
tinct that no room for donbt is left. If the second foot of 
Acantholeberis is compared with the third, as they are figured 
in Lilljeborg, (PI. LYIII) there will be equally little doubt that 
the part there lettered d is the same as the exopodite of the third 
foot. It is also plain that the smaller structure which I have let¬ 
tered d in Wlassicsia, is also the exopodite; or that it is present in 
Ophryoxus and Macrothrix, though still more reduced. This 
can be seen from Lilljeborg’s figures. 
If the part that I have called the first lobe of the endopodite, 
e, be followed through in the same way, there will be just as 
little doubt of its homologies. The large claw of the third 
foot, mounted on e, obviously belongs to the endopodite. This 
claw is clearly the same as that on e of the second foot, and 
this in turn represents the same structure as that which I have 
marked e in the first foot. In the first foot, one would be in¬ 
clined to associate d and e in the exopodite were it not for the 
relations in the feet that lie behind. But a comparison of 
the series quite plainly forbids such an interpretation. If an 
additional reason were needed it might be added that in the 
Sididae, where the exopodite of the first foot is much developed, 
the clasper of the male is derived from the outer branch of 
the endopodite and not from the exopodite. This is an ad¬ 
ditional reason for assigning to the endopodite the large hook 
of the first foot of the male Wlassicsia. 
