294 MANUAL OF ZOOLOGY. 



the female for its entire lifetime. Young females, produced in 

 this way, are also capable for some generations of producing 

 fresh individuals without the influence of a male (partheno- 

 genesis). 



The marine Ostracoda are mostly shallow-water forms, but 

 there are deep-sea types which attain a comparatively gigantic 

 size (nearly an inch in length). 



ORDER II. COPEPODA. Small Crustaceans, having the head 

 and thorax covered by a carapace, and ftirnished with five pairs 

 of natatory feet. Usually there are two caudal locomotive ap- 

 pendages. A distinct heart is sometimes absent (as in the Cyclo- 

 pidce) but is sometimes present. Both marine and fresh- water 

 Copepods are known. 



The larvae of the Copepods are Naupliiform, with unpaired 

 eyes, three pairs of limbs (the future antennae and mandibles), 

 and two terminal setae. Next the maxillae are produced, and 

 then three other pairs of limbs (the foot-jaws and the two front 

 pairs of natatory feet). At the next moult, the larva assumes 

 the Cyclops form, but has at first much fewer limbs and somites. 



In the Cyclops (fig. 145, c), which is one of the commonest 

 of the " Water-fleas," the cephalothorax is protected superiorly 

 by a carapace, and the abdominal somites are conspicuous. 

 In front of the head is situated a single large eye, behind which 

 are the great antennae 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, 

 and 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. Many forms also live in the sea, sometimes in 

 immense numbers. Thus Cetochilus is so abundant in the 

 North and South Atlantic, as to communicate a ruddy tinge 

 to the ocean, and to serve as one of the principal articles of 

 diet of the whale. By good authorities the Ichthyophthira are 

 regarded as merely Copepoda peculiarly modified to suit a life 

 of parasitism. 



DIVISION B. BRANCHIOPODA. The Crustaceans included in 

 this division have many branchiae, and these are attached to 

 the legs, which are often numerous, and are formed for swim- 

 ming. In other cases the legs themselves are flattened out so 



