Geoffroy, the
old historian of the insects of the vicinity of Paris, was the first to
find in the waters of the Seine a small animal resembling one of the
Daphnids. This animal has six short and slender thoracic legs, which
terminate in a hook and are borne on the under side of the cephalic
shield. This latter is provided above with two slender six-jointed
antennae, two very large faceted eyes at the side, and three ocelli
forming a triangle. The large thoraceo-abdominal shield is hollowed out
behind into two movable valves which cover the first five segments of
the abdomen (Fig. 1). The last four segments, of decreasing breadth,
are retractile beneath the carapax, as is also the broad plume that
terminates them, and which is formed of three short, transparent, and
elegantly ciliated bristles. These are the locomotive organs of the
animal, whose total length, with the segments of the tail expanded, does
not exceed seven to eight millimeters. The animal is found in running
waters, at a depth of from half a meter to a meter and a half. It hides
under stones of all sizes, and, as soon as it is touched, its first care
is to fix itself by the breast to their rough surface, and then to swim
off to a more quiet place.
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