800 FRESH-WATER BIOLOGY 



heap. This species really seems to be indifferent to any variation 

 in the pollution of the swampy water in which they normally live, 

 variations and situations that would be fatal to most other Ostra- 

 coda. These forms have also been found in more or less perma- 

 nent ponds fed in part from the drainage from cesspools and from 

 leaky sewers. 



Many bodies of water of different degrees of swiftness are like- 

 wise determinative of different forms. Brooks and rivers are not 

 espacially good habitats, as plant life there is not abundant, and 

 most free-swimming Ostracoda seemingly delight to hang to such 

 supports. However, most forms may be occasionally or adven- 

 titiously found in such waters, as well as in quieter waters. Noto- 

 dromas is typically an inhabitant of pure, fresh pools, although it 

 is a good swimmer, and has the curious habit of trying to support 

 itself on the surface film. 



Among those forms depending upon the Ostracoda in part for 

 food, one must certainly include the young of many fishes, and 

 even the adult Coregonus or whitefish has been found with 

 Candona in the stomachs. Some of the larger marine fishes' seek 

 Ostracoda in the mud. Even aquatic birds may include them in 

 their bill of fare, as, for example, the shoveler or spoonbill duck 

 has been found with Ilyodromus and Cypria in its stomach. 



Owing to the variations in habitat, and the vicissitudes to which 

 most fresh-water Ostracoda are subject, and because of the vari- 

 able and inconstant nature of their surroundings, it is almost im- 

 possible to work out their exact distribution. Cyclocypris laevis, 

 Cypria opthalmica, Cypria exsculpta, and Cypridopsis vidua seem 

 to be cosmopolites in temperate zones, and the most indifferently 

 distributed of any, as they are found in all pools, ponds, swamps, 

 lakes, and rivers of both mountainous and level areas. Their small 

 size permits them to be readily carried about, and their power of 

 adaptation and scavenger habits permit them to thrive in almost 

 any apparently adverse situation. Notodromas, as already stated, 

 appears only in pure standing waters, and mostly in immense 

 numbers. Less abundantly t but still very widely distributed, 

 may be found various species of Candona, Cypris juscata, and Her- 

 petocypris reptans. 



