oh Pe 
Daphnia scheefferi. 
Post-abdomen of female. 
Post-abdomen of male. 
Male antennule. 
Brain and nerves. Inf. c. g., infra-cesophageal ganglion with 
nerves to antenne; c., cesophagus; n. f., frontal nerve; g. 
opt., optic ganglion; m. opt., muscles which move the eye; 
p. f., pigment fleck; n. opt., optic nerve. 
Posterior part of embryo. 
Eurycercus lamellatus. Heart, showing the anterior bifid por- 
tion between the lobes of which is the arterial opening and 
valve. The vaned arrows represent deeper currents while 
the unvaned indicate superficial ones. The dotted line rep- 
resents the position of the pulsating membrane separating the 
venous from the arterial currents and seen in section at (a). 
Daphnia similis. Anterior part of the nervous system seen from 
below. a, optic nerve; b, optic ganglion; c, frontal nerve; 
d, nerve to antennules; e, commissure connecting upper and 
lower cesophageal ganglion; f, nerves to antenne and mandi- 
bles. [After Claus. ] 
