CLADOCERA ; DAPHNIA, OR WATER-FLEA. 267 



to have been transported by the wind. The Branchipi 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. 



ORDER VII. CLADOCERA. 



804. 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 the 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 during the heat of the day. It swims by taking short 

 springs, and feeds on minute particles of vegetable substances, 

 not however rejecting animal matter when offered. There are 

 several curious points, relative to the propagation of these little 

 animals, which are worthy of notice. After the eggs leave the 

 ovaries, they remain in a large cavity between the body and the 

 shell ; here they usually attain their complete development, 

 the young coming forth into the world, in a form very nearly 

 resembling that of the parent. From the transparency both of 

 the eggs and of their containing envelope, the whole process of 

 development may be distinctly seen. At first the eggs are 

 quite round, and seem as if made up of a multitude of minute 

 globules. The shape then alters a little, becoming oval; and 

 these globules augment in number ; but as yet no trace of any 

 body is perceptible. A little afterwards, we see a black spot in 

 the centre, which is the eye, and which is the first organ visible. 



