HABITS OF CYCLOPS AND CYPRIS. 115 



water, but in default of this they will feed upon vegetable sub- 

 stances in a decaying state. There are numerous species belong- 

 ing to this group, of which the Monoculus quadricornis of Lin- 

 naeus (a name improperly changed by Dr. Leach to C. vulgaris) is 

 the type ; it is very variable in its colours, being sometimes red- 

 dish, at others green, bluish, or whitish. It is a very common 

 species. Some of the species (forming the genus Calanus of Dr. 

 Leach, including the C. finmarchianuis of Muller) have the inferior 

 antenna? obsolete, whilst others (forming my genus Canthocampus, 

 having for its type the C. staphylinus,) have the abdomen of the 

 females recurved with a spine beneath at the base, and in some 

 there is but a single egg-pouch (forming my genus Diaptomus), 

 and of which the C. castor is the type. 



2. The Ostracoda (Latreille ; Ostrapoda, Strauss,) have 

 a bivalve shell united by a hinge, and closing during repose ; 

 with the antennae simple and setaceous. They have six legs, 

 and only one eye ; the mandibles and upper maxillae are fur- 

 nished with a branchial plate. (Cypris, the water shell flea,&c.) 

 These insects swim about with great velocity in standing and 

 fresh waters, their bodies being inclosed in the bivalve case 

 united by a hinge, which enables them to close their shells 

 on the approach of danger. According to Jurine, who has 

 observed these insects with much attention, the antennae are 

 employed in swimming, and the two fore legs are used when 

 the animal creeps upon the surface of aquatic plants. He says 

 that the second pair of legs are employed in establishing a 

 motion in the fluid, whereby small particles of food are di- 

 rected to the mouth ; the tail is divided by two fillets, which 

 are folded together when coming out of the shell ; the eggs 

 are inclosed in two large bags at the sides of the body be- 

 neath the shell : the female is occupied for about twelve hours 

 in depositing them upon aquatic plants. As in the Cyclops, 

 Jurine observed that several generations are capable of being 

 produced without more than a single coupling having pre- 

 viously taken place. 



3. The Cladocera (Latreille), have also the shell bivalve 

 and a single eye, but without a hinge, and terminating in a 



