24 



NATURAL HISTORY OF ARTHROPODS. 



motion depends upon the size of the antennules. In Cyclops they are of moderate size, 

 and are actively used in swimming, though the tail is employed for sudden leaps, and 

 often aids ordinary progress. In the Calanid^ the antennulse are very long — often 



FlQ. 30. — Calanus pavo. 



longer than the animals — and moved by muscles of corresponding strength. Single 

 strokes propel the animal to a considerable distance. This power, and the relatively 

 large size of these members of the Copepoda, give a sort of dignity to their movements. 

 They remain quietly at rest for some minutes, flapping the wing of the maxilla in order 

 to keep up a current of water for respiration, and perhaps to 

 bring small bits of food to the mouth ; then suddenly dart a 

 little way, probably to seize some victim, and then return once 

 more to rest. Their vigor is well seen on trying to catch 

 one with the dipping-tube. As soon as the animal feels the 

 rush of ascending water it darts off with a single powerful 

 stroke of the antennules, and so escapes repeated attempts at 

 capture. 



At the other end of the series from Calanus, so far as re- 

 gards locomotion, stands Canthocamptus, a member of the 

 family Haepactid^ (Fig. 31), whose antennules are very 

 short, and their action aided by a constant wiggling of the 

 body in locomotion making their mqtion almost worm-like. 



Cyclops, both in structure and habits, stands between these 

 extremes. It is usually found, like Calanus, in the free water, 

 though, like Canthocamptus, it may burrow in among weeds 

 and vegetable dfebris. Often it lies suspended in the water, 

 at rest save for the fluttering of the maxilla, or it may rest by 

 clinging to some support. It may move slowly and steadily 

 by- rapid strokes of its thoracic feet, or dart an inch or more 

 by sudden strokes of its antennules. These movements seem to catch the prey, 

 which consists of rotifers, Infusoria, other Crustacea, in short, any animal not too large 



Fig. 31. — Canthocamptus 

 cavemarum. 



