Structure of the Larva of Epischura Lacustris. 545 
minute forms. It has seemed best to me, on this account, to 
publish certain facts which have already been worked out, al¬ 
though this paper must be considered as a communication pre¬ 
liminary to a more extended paper. 
The peculiar armature of the furca, which can be recognized 
quite easily in all except the earliest stages, makes it possible 
to distinguish quite readily between the larval forms of Epis¬ 
chura and those of other copepods. The characteristic form of 
the first maxillipede is developed very early, and by this fea¬ 
ture alone one can frequently pick out Epischura larvae with a 
considerable degree of accuracy. 
In this paper I will treat of only two structures, the male 
abdomen, and the male fifth feet. 
The dissections on which the following facts are based were 
made by Mr. E. E. Hemingway, under my direction, and much 
credit is due him for the skill which he acquired in distinguish¬ 
ing the larvae of Epischura from those of other copepods, and 
for the patience which he exercised in making the difficult dis¬ 
sections. 
THE MALE ABDOMEN. 
In the abdomen of the mature male the second and third seg¬ 
ments are produced to the right, and from the fifth segment 
there are two projections to the right, one spatulate, and the 
other dentate. (Plate XII, Fig. 5.) 
In the larval abdomen the segments of the abdomen retain 
their symmetry until the animal has reached very nearly the 
mature form. In plate XII, Figs. 1, 2, 3, and 4, are shown the 
1, 3, 4, and 5 segment stages,—the last having the same num¬ 
ber of segments as the mature animal. Up to and including 
the four segment stage there is nothing in the form of the seg¬ 
ments to distinguish these larvae from the larvae of other copepods, 
as they are entirely symmetrical. In the last stage, however, the 
bend to the right is very marked: the projection on the second seg¬ 
ment is much like that in the mature animal, and the same thing 
is true of the projections on the fifth segment: the third segment 
has a pronounced swelling on the right side, but is quite dif¬ 
ferent from the form in the mature animal. The specimen from 
