196 Fortieth Annual Meeting 



vegetation in the lake and on its shore had the usual zonal 

 arrangement, which was not uniform in its distinctness in 

 different places. The distribution of aquatic plants had a 

 marked influence on the distribution of fish in the lake, and 

 each of these plant zones, then, with the abyssal portion of 

 the lake surrounded by them, formed distinct fish habitats. 

 Each of these will be considered as much in detail as pos- 

 sible. We named the zones from the most conspicuous 

 plants which they contained, and our main fish habitats were 

 then as follows : ( 1 ) The abyssal or deep-water region, 

 (2) the pondweed zone, (3) the shoal or rush zone, and 

 (4) the sedge zone. 



1. THE ABYSSAL OR DEEP-WATER REGION 



The abyssal part of the lake was considered to be that 

 portion of it where the water was deeper than about 25 

 feet, and hence it had a maximum depth which was that 

 of the lake, a little over 100 feet. This included the greater 

 part of the lake, all but the shoal and the pondweed zone, 

 which together occupied a strip of water averaging perhaps 

 near three hundred feet in width. This deep water area 

 had the following important characteristics which influenced 

 fish-life : absence of all but microscopic plants, chiefly 

 diatoms ; a bottom soil rich in humus, increasing in amount 

 in proportion to other ingredients as the deepest part of the 

 lake was approached ; water quite stagnant and cold below 

 the thermocline (which from a set of temperature readings 

 made in August, seemed to lie at about 25 feet) ; and with 

 little, if any, illumination in the deepest parts; and with 

 considerable water pressure. A peculiar association of 

 invertebrate forms existed here in the bottom soil, composed 

 chiefly of large, red larvae of midges (Chironovius), which 

 were found numerous at all times and at all depths in this 

 region. No investigations of the plankton were made, but 

 many entomostracans and phantom larvae (Sayomyia) were 

 noted, rather incidentally. 



The following species of fish were caught here : White- 



