COMMUNITIES IN OTHER INLAND WATERS 365 



7 protozoans, 16 rotifers, 20 cladocerans, 11 copepods, and 1 insect 

 larva. The only ones appearing in great numbers are Daphnia long- 

 ispina and Cyclops strenuus and serrulatus; the copepods Diaptomus 

 bacillijer and Diaptomus denticornis are widespread. The limnetic 

 forms, however, are also found near the shores, and many littoral 

 forms mix with the plankton. The slight warming of the shore water 

 and the absence of a luxuriant littoral flora may contribute to this 

 fact. A number of alpine animals develop a reddish color like the arctic 

 copepods. Red coloration is also more frequent in copepods of low 

 altitudes and in temperate regions, if they appear in early spring when 

 water temperatures are low. 



The fact that animals living in polar and alpine lakes exhibit 

 similar trends among the many adaptations which appear is explained 

 in part by the influence of similar environmental factors. Another 

 explanation, however, is needed for the fact that stenothermal cold- 

 water animals in the alpine lakes and of the far northern waters often 

 represent the same species; the inhabitants of these regions are 

 homologous, and not merely analogous, while in the intermediate 

 zones, in contrast with their ubiquitous companions, such stenothermal 

 species are isolated in cold moor ponds or mountain lakes. Many* are 

 to be considered as relicts of a fauna which retreated with the glaciers 

 into northern or alpine waters. They disappeared in intermediate 

 areas, except where cold springs, cold water basins, or the pedon of 

 lakes afforded them a more or less secure refuge. 



Other inland waters. — Some inland waters differ markedly from 

 the ordinary fresh-water environments. These include waters which 

 contain in solution certain elements of organic or mineral origin in 

 considerable amounts and hence are known as humus waters or salt 

 waters; others may be distinguished by constant low temperature as 

 in mountain springs or by the high temperatures of thermal springs. 

 The fauna of cave waters characterized by the absence of light will be 

 considered together with the rest of the cave fauna, but life in springs 

 will be discussed in this section. 



Communities associated with humus waters. — Sphagnum bogs 

 are formed over impervious clay as the last step in the transition from 

 ponds to dry land. Sphagnum and the associated plants are intolerant 

 of lime. Peat moors develop in non-calcareous regions, with heavy 

 precipitation, which are poor in lime and nutriment; they are par- 

 ticularly abundant in the north temperate region in Europe and North 



* Cladocera, e.g., Chydorus piger, and Alona intermedia, the copepods Diapto- 

 mus laciniatus, and Diaptomus bacilijer, Canthocamptus cuspidatus and C. 

 zschokkei, and the water mite Hygrobates albinus, and Planar ia alpina. 



