184 MANUAL OF ZOOLOGY. 



are the great antennas and the antennules. The feet are five 

 pairs in number, each consisting of a protopodite and a seg- 

 mented exopodite and endopodite, usually furnished with hairs 

 *nd forming an efficient swimming apparatus. The young 

 pass through a metamorphosis, and are not capable of repro- 

 ducing the species until after the third moult or change of 

 skin. The female Cyclops carries externally two ovisacs, in 

 which the ova remain till they are hatched. A single congress 

 with the male is apparently sufficient to fertilise the female 

 for life. 



The Copepoda, or Oar-footed Crustaceans, are all of small 

 size, and are of common occurrence in fresh water in all parts 

 of Europe. 



DIVISION B. BRANCHIOPODA. The Crustaceans included in 

 this division have many branchia?, and these are attached 

 to the legs, which are often numerous, and are formed for 

 swimming. The body is either naked, or is protected by a 

 carapace, which may enclose either the entire body, or the 

 head and thorax only. The mouth is provided with organs of 

 mastication. 



The Branchiopoda comprise the Cladocera, the Phyllopoda, 

 and probably the Trilobita, though this order departs in many 

 respects from the above definition. The Merostomata may 

 be considered along with these, though these, too, are in many 

 respects peculiar. 



ORDER I. CLADOCERA. The members of this order are small 

 Crustaceans, which have a distinct head, and have the whole 



Fig. 51. Cladocera. Daphnia pulex, the common Water-flea (male), greatly 



enlarged. 



of the remainder of the body enclosed within a bivalve cara- 

 pace, similar to that of the Ostracoda. The feet are few in 

 number (usually four or five pairs), and are mostly respira- 

 torv, carrying the branchiae. Two pairs of antennas are 

 present, the larger pair being of large size, branched, and 

 ting as natatory organs. 



