CRUSTACEA. 209 



within which the ova, after being fertilized, undergo the earlier stages of 

 their development. The Cyclops is a very active creature, and strikes the 

 water in swimming, not merely with its legs and tail, but also with its 

 antennae. The rapidly-repeated movements of its feet-jaws serve to create 

 a whirlpool in the surrounding water, by which minute animals of various 

 kinds, and even its own young, are brought to its mouth to be devoured. 



606. The tribe of Branchiopoda also is divided into two Orders, of 

 which the Cladocera. present the nearest approach to the preceding, hav- 

 ing a bivalve carapace, no more than from four to six pairs of legs, two 

 pairs of antennae, of which one is large and branched and adapted for swim- 

 ming, and a single eye. The commonest form of this is the Daphniapulex, 

 sometimes called the 'arborescent water-flea,' from the branching form 

 of its antennae. 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 sub- 

 stances, not, however, rejecting animal matter when offered. Some of 

 the peculiar phenomena of its reproduction will be presently described 

 ( 609). 



607. The other order, Phyllopoda, includes those Branchiopoda 

 whose body is divided into a great number of segments, nearly all of 

 which are furnished with leaf-like members, or * fin-feet.' The two 

 Families which this order includes, however, differ considerably in their 

 conformation; for in that of which the genera Apus and Nebalia are rep- 

 resentatives, the body is inclosed in a shell, either shield-like or bivalve, 

 and the feet are generally very numerous; whilst in that in which contains 

 Branchipus and Artemia, the body is entirely unprotected, and the 

 number of pairs of feet does not exceed eleven. The Apus cancriformis, 

 which is an animal of comparatively large size, its entire length being 

 about 2% inches, is an inhabitant of stagnant waters; but although occa- 

 sionally very abundant in particular pools or ditches, it is not to be met- 

 with nearly so commonly as the Entomostraca already noticed. It is 

 recognized by its large oval carapace, which covers the head and body like 

 a shield; by the nearly cylindrical form of its body, which is composed of 

 thirty articulations; and by the multiplication of its legs, which amount 

 to about sixty pairs. The number of joints in these and in the other ap- 

 pendages is so great, that in a single individual they may be safely esti- 

 mated at not less than two millions. These organs, however, are for the 

 most part small; and the instruments chiefly used by the animal for loco- 

 motion are the first pair of feet, which are very much elongated (bearing 

 such a resemblance to the principal antennae of other Entomostraca, as to 

 be commonly ranked in the same light), and are distinguished as rami or 

 oars. With these they can swim freely in any position; but when the 

 rami are at rest and the animal floats idly on the water, its fin-feet may 

 be seen in incessant motion, causing a sort of whirlpool in the water, and 

 bringing to the mouth the minute animals (chiefly the smaller Entomos- 

 traca inhabiting the same localities) that serve for its food. The Bran- 

 chipus stagnalis has a slender, cylindriform, and very transparent body 

 of nearly an inch in length, furnished with eleven pairs of fin-feet, but is 

 destitute of any protecting envelope; its head is furnished with a pair of 

 very curious prehensile organs (which are really modified antennae), 

 whence it has received the name of CheirocepJialus; but these are not 

 used by it for the seizure of prey, the food of this animal being vegetable, 

 and their function is to clasp the female in the act of copulation. The 



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