8 ILLINOIS BIOLOGICAL MONOGRAPHS [8 



sively tabulated; the dissolved gases of the water have been extensively 

 studied, and the seasonal variations carefully recorded. Thus, by the 

 foundations laid down by these investigators, the road has been paved for 

 further studies of the lakes of southern Wisconsin, and it must be admitted 

 that, in spite of the excellent beginning that has been made, all the work 

 so far has been only a beginning. Our knowledge of the lakes in question 

 is still only skin deep — surface deep — if indeed it is not merely a ripple on 

 the surface. The work of Birge and Juday has been followed by the studies 

 of Pearse on certain fish occurring in the Madison waters, and by Mutt- 

 kowski with his quantitative and qualitative study of the fauna of Lake 

 Mendota, with special reference to insect life. Concerning the Waukesha 

 county group of lakes, nothing has been published outside of the work of 

 Birge and Juday, excepting only a few records of fish foods furnished by 

 the writer to Pearse and included in one of his papers (43). 



The present paper is, in a way, the result of circumstances. Having 

 lived in Waukesha county for over twenty summers, and having, during 

 the last twelve years, his own private laboratory for carrying on investiga- 

 tions, the present writer has attempted to avail himself of the opportunities 

 lying literally at his door. A serious study of the fishes of the region was 

 begun in 1914 when, as a graduate student at the University of Wisconsin, 

 the writer undertook an intensive study of the life history of the cisco 

 (Leucichthys artedi (LeSueur) ) in Lake Mendota and in the Waukesha 

 county lakes which contain the species. A collection of the various species 

 of fishes of the region was begun long before this date in an effort to ascer- 

 tain what fishes inhabited the lakes and rivers. While the original idea 

 encompassed only a listing of the species, this was enlarged in 1915 to 

 include an intensive study of every species possible. Thus the study of the 

 biology of the cisco was subordinated to a study of the biology of the fishes 

 of the region, and forms one of a series of studies dealing with ecological 

 life history investigations of individual species. 



This series of papers, of which this is the first, purports to be a series of 

 ecological studies made upon the fishes found within the boundaries of 

 Waukesha county, Wisconsin, together with certain observations made 

 upon identical species in other regions of the state where opportunities or 

 facilities proved more advantageous for carrying on the work. The data 

 presented are entirely original unless otherwise specifically stated. These 

 include the results of something over one hundred gas analyses to deter- 

 mine the position of the thermocline in various lakes at different times of 

 the year in order to ascertain its effect upon the distribution of the fishes; 

 over two thousand H-ion determinations, accompanied in some cases by 

 oxygen determinations, in an effort to discover if either of these factors is 

 responsible for certain behavior phenomena; thousands of temperature 

 readings at all depths of water, and many visibility readings by means of 



