356 



this was in the lower part of the lake, and not above the middle as in 



the latter part of July 1922. 



Bottom Dissolved Oxygen, Mid-chaxnkl, Middle Peobia Lake. 1920-1922 

 Midsummer Figures, Parts per Million 



* Miles below Lake Michigan. 



Sm.-\ll Bottom Animals 



The all-zone list of small bottom animals from the middle lake 

 contained 23 species in 1932 compared with 19 from the upper lake 

 the same season (Table 1, p. 358). Though varietj' of species was 

 least both in the middle and the upper lake at the channel stations, it 

 was there that the greatest relative increase occurred : i. e., from 8 

 species in the upper to 11 species in the middle lake in the same period. 

 In the wide waters the 1922 hauls yielded in all 21 species compared 

 with 18 from the upper lake. The increases over the upper lake lists 

 were largely due both in the channel and in the wide waters to in- 

 ci'eased variety of the less tolerant snails and midge larvae, the first 

 of these two groups rising to a total of 10 species for the middle lake 

 as a whole in the summer of 1922. 



