108 THE LIFE OF DEVILS LAKE 



curs commonly in winter in Green Lake, Wis. but is rare in sum- 

 mer ; but is found in the cold waters of the Great Lakes thruout the 

 summer. In the Devils Lake complex, however, it is common at 

 certain times in summer at high temperatures.** Brachionus 

 plicatilis is given as a marine and brackish water form in Brauer 

 (1912), but here it occurs in both fresh and alkaline waters. These 

 instances might be multiplied, but are sufficient to illustrate how 

 much we have yet to learn regarding the distribution and adapta- 

 tion of aquatic life. 



It is unsafe therefore to attempt at present anj' delimitation of 

 life zones, or to draw conclusions regarding the origin of any fauna 

 or flora, based upon their plancton components. 



This opinion agrees with that of other workers in this field. 

 Thus Jennings, in Ward & Whipple (1918), emphasizes the essen- 

 tially cosmopolitan character of rotifers, whose distribution is deter- 

 mined by the character of their environment, rather than its geo- 

 graphical position; while the former factor is ineffective in the case 

 of many species, which can inhabit fresh and brackish, or even sea 

 water alike. And Edmondson (1912) in his account of the Protozoa 

 from some high mountain lakes in Colorado, says (p. 67) "By com- 

 paring the following list with the protozoa reported from sea-level 

 in tropical Tahiti (Science, September 9, 1910), there will be seen 

 not only the latitudinal but also the great altitudinal range which 

 many of our species have." In a letter to the writer (Augu.st 21, 

 1923) Prof. C. J. Elmore who has worked on the diatoms of Devils 

 Lake says: 



"I have never been able to find that certain species of diatoms 

 are northern and others southern. A good many species that are 

 common in this region (Nebraska) were first described as Arctic 

 diatoms . . . As to locality, I have found just the same species 

 in collections from India that I find at home." 



Birge, in Ward & Whipple (I.e.), says (p. 687) of the Clado- 

 cera, "The geographical distribution . . . offers little of inter- 

 est that can be stated in a brief sketch, chiefl.y because the species 

 are so widely distributed. Some are . . . cosmopolitan. A 

 majority (of those) found in this country are found also in Europe." 

 The study of our fo7'nis has not gone far enough to enable us to 

 speak of the local distribution of each species within the area which 

 it covers, but it is known that the rare species are very irregularly 

 distributed. On the whole the fauna of the various regions of the 

 country is strikingly similar, but with some forms peculiar to each 

 region. 



Sharp in the same place says (p. 800) "Owing to the varia- 

 tions in habitat, and the vicissitudes to which most fresh water 



•♦Over 20° C. 



