CLADOCEKA. 



285 



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 



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spiny-tailed water-flea, Acanthocercus (muck enlarged). 



the head are antennas (R, T). The first pair of antennas are small and simple. 



The jaws consist of the mandibles and the first pair of maxillae, the second 



pair of maxillre 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 ai'e 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 typo 



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). 



