802 FRESH-WATER BIOLOGY 



Migration from one region to another may be brought about by 

 swimming beetles such as Belostoma, Gyrina, etc. Cyclocypris has 

 been observed 'hanging to the legs of such beetles, even though the 

 beetles were actively using their legs. Birds may also be of great 

 importance as carriers of both the minute flora and fauna of a 

 region. The eggs of Ostracoda, and even the animals themselves, 

 may be carried about on the bills and feet of aquatic birds, and 

 even fishes may act as a means of transport from one region to 

 another. 



The Ostracoda belong to the plankton. In common with certain 

 other organisms, such as Rhizopods, Diatoms, Hydra, etc., they 

 appear in the plankton under certain conditions of temperature 

 and food, and hence are said to belong to the adventitious plank- 

 tonts, in distinction to such forms as Cyclops, which are always 

 in the plankton, and therefore called continuous planktonts, 

 or those that appear periodically, as Daphnia and some Rotifera, 

 when they are called periodic planktonts. For evident reasons the 

 creeping or burrowing forms rarely occur in ordinary plankton 

 catches. 



According to their habitat and mode of locomotion, the ostracod 

 adventitious planktonts may be classified as follows : 



A. Free swimming. 



1. Limnetic, with surface habits, as Notodromas monacha. 



2. Free swimming, below the surface, as Cypris laevis, 



C. incongruens, C. vidua, etc. 



B. Creeping or burrowing. 



1. Creeping on water plants or ooze, as Herpetocypris rep- 



tans. 



2. Burrowing in the slime or ooze, as Candona Candida, 



and Limnicy there. 



Little is surely known of the duration of life of special forms. 

 Some species are present the entire year. They live over the 

 winter, and are also found in different developmental stages under 

 the ice. It is an easy matter to collect mud under ice in midwinter, 

 place it in a small aquarium jar and set in a moderately warm 

 place, and very shortly find plenty of Cypris, Cypria, and Candona. 



