DISTRIBUTION OF SPECIES. gj 



ber of collections at different times without finding a single 

 specimen of this genus, and I had concluded that it was en- 

 tirely absent from the lake, but in 1900 I found two or three- 

 individuals. This absence of Diaptomus is one of the most pecu- 

 liar facts in distribution which I have run across. Pelican 

 lake is a large body of water, with a maximum depth of about 

 twelve and a half meters and with a large amount of plankton. 

 It is considered a fine fishing lake, and one would expect an 

 abundance of the ordinary Crustacea of the plankton. 



In the collections on the northern lakes work was carried on 

 in two distinct drainage areas and I was interested to see 

 whether any difference in the faunae and florae of the two areas 

 could be detected. As I expected, there was no difference ex- 

 cept that due to the difference in depth and general physical 

 conditions of particular lakes. 



Generally speaking, the result of these collections was to con- 

 firm the statements made by other authors and myself that there 

 is practical uniformity in the fauna and flora of lakes over wide- 

 extents of territory, except as differences in depth produce con- 

 ditions of especial character. It is strange, however, that with 

 this general uniformity there should be cases of isolation like 

 that of Diaptomus siciloides in Cedar lake or of failure of oc- 

 currence like the lack of Diaptomus in Pelican lake. 



In the discussion of the means by which organisms are dis- 

 tributed from lake to lake I am inclined to think that too much 

 importance has been attached to the work of water fowl. While, 

 doubtless, it is a proven fact that water fowl carry organisms, 

 seeds, and eggs, from lake to lake, I imagine this is a very 

 minor factor in distribution. It is a fact that communicating 

 bodies of water are pretty certain to have the same fauna and 

 flora. This is very noticeable in the lakes in Michigan which 

 are connected with Lake Michigan, for their faunae are iden- 

 tical with that of the larger lake. The same is true of Lake 

 Winnebago and its connecting waters. When lakes are pretty 

 distinctly separated from each other, there is likely to be a dif- 

 ference in fauna and flora. In other words "isolation" plays 



