256 THE FOOD OF ANIMALS 



It not infrequently makes its appearance in spring in small tem- 

 porary accumulations of fresh water, and is native to many parts 

 of the world. The greater part of the well-segmented body is 

 covered above by a large overlapping oval shield, while the under 

 side bears the mouth, provided with three pairs of jaws, and a 

 large number of leaf-like feet. The animal swims on its back, 

 being, as it were, paddled along by the perpetual swinging of the 

 feet backwards and forwards. There is a longitudinal groove 

 between the rows of limbs, along which food is conducted to the 

 mouth, and even when swimming no doubt a certain amount of 

 food is passed along this, in the current of water set up by the 

 feet. Apus is also able to browse on the surface of the mud 

 or of water-plants, much in the same way as has been described 

 above for Cyclops. 



The second sub-group of the Phyllopods is that of the Water- 

 Fleas (Cladocera), much smaller creatures than their immediate 

 relatives, and including some marine forms, though most live in 

 fresh water. A common type is Daphnia (see vol. 'i, p. 419), a 

 short -bodied creature, of which all but the head is enclosed in 

 a bivalve shell. Swimming in a jerky sort of way is effected 

 by means of the relatively enormous second pair of feelers. 

 There are but two pairs of jaws, and behind this a small num- 

 ber of flattened limbs, which by their constant movement maintain 

 a flow of water along the under side of the animal, which serves 

 both for breathing purposes, and also brings with it minute or- 

 ganisms and particles which serve as food. 



