1879 ] Fresh-Water Entomostraca. 621 
largely into the diet of fish, even of the larger varieties. The 
larger portion, of the Entomostraca, numerically at least, are 
vegetable feeders and live on the minute particles of matter float- 
ing in the water, which otherwise would tend to render our waters 
impure. The snails wipe clean the stones and water-plants, and 
the scavenger fishes remove the carrion, but it remains for minuter 
forms to search carefully each drop and remove the particles, 
microscopic even to the thousand eyes of the dragon-fly larva. 
Thus the Séda (Plate 111) in swimming uses the branchial feet 
within the shell-valves, not only in taking the necessary air from 
the water, but, by creating a counter current between the bases of 
the feet, particles of food are constantly brought within reach of 
the jaws. In common with low forms of animals in general, the 
processes of reproduction are often curiously anomalous. Con- 
gress of the sexes is in many cases unnecessary for many genera- 
tions, and some forms, especially the Artemia, or “ brine shrimp,” 
seem unusually susceptible to changes in their environment. 
Males are often produced only in certain seasons of the year or 
under certain climatic conditions. 
In the Daphnia the females produce young by simple budding 
from the ovary, but in the winter the ovum is enclosed between 
the valves of the carapace, which is removed at each molt, and it 
is thus enabled to resist the severity of the cold season. Speaking 
of the molt it is interesting to note that every hair, even to the 
finest filament, throws off a sheath, so that the cast-off integu- 
ment is a perfect copy of the animal from which it came. In the 
higher forms the eggs are carried during the later stages of em- 
bryonic existence in double or single sacs extending beneath or 
on either side of the abdomen. In the Daphnia and other forms 
enclosed in a carapace the animal is oviparous, and the young 
can be seen within the shell in a cavity above the abdomen for 
some time before they are sent out to paddle their own crystal 
canoe. They may be removed from the parent without inconve- 
nience. In the larger sub-division, the Lophyropoda, the chief 
organs of locomotion are one or both pairs of antennz, though — 
natatorial feet are never wanting. The antennz also serve as pre- 
hensile organs in the Cyclopoidea, while the feet throughout the 
whole legion have branchial filaments. 
Every one who has used the microscope has met with some of 
these animals, and we will mention a few forms. If water, taken — 
from the clear surface of a lake ona sunny day, be carefully ob- 
