CLADOCEKA. 
takes its name. At the front of the head (A) is a large compound eye (O), 
and the branched and plumed appendages projecting from beneath the sides of 
the head are antennae (R, T). The first pair of antennae are small and simple. 
The jaws consist of the mandibles and the first pair of maxillae, the second 
pair of maxillae being obsolete in the adult. The 
thorax comprises five segments, each bearing a pair 
of leaf-like swimming-limbs. The abdomen consists 
of three segments and is limbless. The males of 
Acanthocercus are smaller than the females and 
much rarer, being generally met with in the 
autumn. Eggs are laid both in summer and winter 
and are passed into a brood-pouch, separating the 
upper surface of the thorax from the backward 
extension of the carapace. Here the summer-eggs 
hatch, but the winter. set are enclosed in a kind of 
capsule developed from part of the carapace. This capsule, called the ephippium, 
is cast off with the next moult of the mother’s integument, and falling to the bottom 
of the water gives exit to the embryos, which hatch in its interior. Another type 
is the glassy Leptodora hyalina, so called on account of its semi-transparency, which 
inhabits the open water of fresh-water lakes. The shell is so much reduced as 
scarcely to envelop the animal. 
EGG-CAPSULE OR Ephippium OF WATER- 
FLEA, Acanthocercus (much enlarged). 
