CHIROCEPHALUS. ORDER CLADOCERA. 269 



which they are chiefly found, are called " clearers," as the liquid 

 becomes clear in them ; and this is attributed by the workmen to 

 the rapid motion of the feet of these little creatures ; and so firmly 

 are they persuaded of this, that, according to Mr. Rackett, they will 

 transport a few brine-worms, as they call them, from one saltern 

 in which these animals are abundant, to another in which they 

 do not make their appearance. Nearly allied to this is the Chi- 

 rocephalus ; of which the several species are found, often in great 

 numbers, in small pools, especially after heavy rain ; sometimes 

 even in those which are left on the uneven surfaces of stones, 

 the eggs, which are inclosed in a strong shell, seeming to have 

 been transported by the wind. The Chirocephali generally 

 swim on their backs ; and their short lamellar feet, which are 

 unfit for walking, are then kept in an undulatory motion, that 

 sends forward a current of water, along a channel hollowed in 

 the lower side of the body, to the mouth, and thus supplies the 

 animal with food. At other times, they swim more forcibly, by 

 alternate lateral strokes of the tail upon the water. The British 

 species (Fig. 603) measures more than an inch in length, and is 

 a very beautiful creature. 



ORDER VIII. CLADOCERA. 



879. The Order CLADOCERA consists of those minute Crus- 

 tacea answering to the foregoing description, which have the body 

 inclosed in a bivalve shell. These belong, for the most part, to 

 <he genus Daphnia; of which the common species, Daphnia 

 pulex (which has also received the name of Monoculus from its 

 single eye), is commonly termed the Arborescent Water- Flea, 

 from its power of leaping, and from the branching form of its 

 antennae, which serve as oars. It is very abundant in many ponds 

 and ditches, coming to the surface in the mornings and evenings, 

 and in cloudy weather ; but seeking the depths of the water dur- 

 ing the heat of the day. It swims by taking short springs, and 

 feeds on minute particles of vegetable substances, not however re- 



