SUPPLEMENTARY NOTE 



A copy of the second part of Ekman's paper ('15) has 

 become available as these pages go to press. The quantitative 

 studies (pp. 401-41 1, pi. 6-14) are very interesting and clearly 

 show the value of this kind of investigation. Following Peter- 

 sen's method, Ekman has illustrated the number of individuals 

 collected from an area of 5 dm. square. This unit area is 25 

 times greater than the unit area studied in Oneida Lake ( i dm. 

 square or about 16 square inches). The Swedish lake is also 

 much deeper than Oneida Lake and comparisons are not 

 therefore strictly comparable. The results obtained from a 

 study of this deep lake are of special interest for comparison 

 with the shallower Oneida Lake and a few of Ekman's are 

 shown in the table below : 



The table does not show a decrease in number of indi- 

 viduals with depth as was the case in Oneida Lake, but rather 

 an increase with depth. It will be noted, however, that the 

 greatest number of individuals, 351 and 364, occurred at 

 depths of 31 and 112 meters, so that depth does not seem to be 

 important in this lake. Compared with Oneida Lake the 

 number of individuals are nearly twice as numerous in the 

 American lake as in the Swedish lake. Similar studies on our 

 deep lakes, Cayuga, Seneca, etc., would be of very great 

 interest for comparison with Lake Vatter. 



252 



