Structure of the Larva of Epischura Lacustris. 547 
The youngest specimen in which we have been able to obtain 
a male fifth foot was the one from which the abdomen was 
drawn for Fig. 2, Plate XII. This was in the three segment 
stage. The fifth feet are shown in Plate XIII, Fig. 1. In this 
figure as in Fig. 4, the feet were drawn from the side opposite 
to that from which the other figures were drawn, so that the 
relative position of the feet is reversed. In this figure it will 
be noticed that the left foot consists of a basal segment, and 
both an exopodite and an endopodite, each consisting of a single 
segment. The right foot consists of a basal segment, a one- 
segmented exopodite, and a process on the basal segment which 
apparently represents an endopodite. The fifth feet shown in 
Plate XIII, Fig. 2, represent practically the same stage of de¬ 
velopment as that in the first figure, but in this the right foot 
has an evident endopodite. 
Figure 3 represents the fifth feet of an individual in which 
the abdomen had reached the four segmented stage. The ex¬ 
opodite of the left foot in this specimen is composed of two seg¬ 
ments, the outer segment having three spines, while only one 
was found in the lower stages. The endopodite is still of a 
single segment, but has grown long and slender. In the right 
foot the exopodite is divided into two segments, and the en¬ 
dopodite has disappeared. 
In figure 4 is shown the fifth feet of the individual from 
which the abdomen in Plate XII, Fig. 4, was drawn. In the 
right foot the exopodite is reduced from two segments to one, 
has become triangular or conical in shape, and is strongly re- 
flexed. In the left foot the exopodite has the concave inner 
margins seen in the mature animal, and the terminal segment 
is armed with spines and hairs much as in the last stage. The 
endopodite has become greatly curved and is clearly to become 
the “curved process ’’ of the basal segment as described in the 
mature form. 
It is evident, then, that the fifth feet of Epischura lacustris 
are to be explained morphologically in this way. Of the two 
segments of the right foot, the first is the basal segment, and 
the second is the reduced exopodite, the endopdite having disap¬ 
peared, although existing in lower stages. In the left foot the 
