330 Merrill—Structure and Affinities of Bunops Scutifrons. 
FIFTH LEG. 
PI. XV, Fig. 5. 
The fifth leg consists of the exterior ramus and the maxil¬ 
lary process only. The outer ramus is well de\ eloped and has 
two setae, the larger one curving around the gill-sac and the 
other straight. The maxillary process has three setae. One is 
long, borne on a separate lobe, and there are two short setae at 
the side. The setae are all densely ciliated. 
The legs of Bunops differ from those of the other genera of the 
Macrothricidce , in that the four anterior legs all show traces of 
lobing of the inner branch, and that all four legs possess setae 
arranged in distal and proximal rows. 
INTERNAL ORGANS. 
The specimens of Bunops scutifrons which I obtained from 
Minocqua were simply preserved in alcohol, and the internal or¬ 
gans were not in very good condition for study. In early July, 
1893, a few specimens of the species were found at Madison, Wis., 
and a short study of the general internal structure was made. 
The animal is hyaline and all of the internal organs can be 
seen very plainly. 
The intestine is a simple tube, with no glands or convolutions, 
its walls are rather thm, and its contents give it usually a yellow 
color, rendering it a very conspicuous object in contrast to the 
colorless organs along which it lies. The heart (PI. XIV, 
Fig. 4.) has the usual form of a rounded sac, having the venous 
ostia placed as usual. The crest of the valves is so developed 
that the axis of the heart instead of lying parallel to that of 
the body, is at right angles to it, the anterior end of the heart 
being dorsal. A short arterial trunk is connected with it. 
The blood is of a pale yellow color, and it seems devoid of 
corpuscles. This fact has already been noted by Weismann in 
Lathonura rectirostris. It is not improbable that the corpuscles 
are wanting in a large number of the Cladocera, but no exact 
observations on this subject have as yet been made. 
