Lake Maxinkuckee, Physical and Biological Survey 107 



Horizontal distribution: — A comparison of the tables for sta- 

 tions I and II shows that, with two exceptions, the quantity of 

 plankton obtained at Station II was smaller than that obtained the 

 same week and from similar depths at Station I. The differences, 

 however, are comparatively small, which shows that the local pe- 

 culiarities at the former had relatively little effect on the plankton. 



The hauls made at the five stations in the main basin of the 

 lake, besides the two regular ones, showed that the plankton was 

 very evenly distributed. 



Vertical distribution: — The plankton was confined almost 

 wholly to the upper 12 meters. This included the thermocline 

 which extended from 9 to 12 meters. Undoubtedly the region 

 below this depth remained almost tenantless because of the chemi- 

 cal condition of the water. Only Corethra larvae were found regu- 

 larly below the thermocline. 



A little more than 48 per cent, of the entire quantity of plank- 

 ton was found in the 0-1 meter layer. As might be expected, this 

 was preeminently the region for phytoplankton. The Crustacea 

 were represented by a few Cyclops and a considerable number of 

 nauplii. The 0-3 meter stratum contained 68 per cent, of the en- 

 tire quantity. Ceriodaphnia lacustris and Diaphanosoma brachyu- 

 rum were found mainly in the 1-3 meter stratum. Diaptomus 

 minutus and Daphnia retrocurva seemed to prefer the region be- 

 tween 3 and 12 meters. Daphnia pulicaria was most abundant 

 in the region of the thermocline, or between 9 and 12 meters. 

 Cyclops and nauplii appeared more or less abundantly throughout 

 the upper 12 meters. 



Only one set of observations was made at night. The quantity 

 of plankton obtained from the 0-1 meter stratum at night was 

 smaller than that obtained during the previous afternoon but there 

 was a marked increase in the Crustacea. Epischura lacustris, 

 Leptodora hyalina and adult Daphnia retrocurva were found in 

 this stratum at night but never in the day catches. Also there 

 was a larger number of adult Cyclops than was usually found in 

 the daytime. 



I am indebted to Prof. C. Dwight Marsh for the following list 

 of Copepoda : 



Cyclops leuckarti Claus; Cyclops prasinus Fischer; Diaptomus 

 minutus Lilljeborg; and Epischura lacustris Forbes. 



The following Cladocera were collected: Daphnia pulex puli- 

 caria Forbes, Daphnia retrocurva Forbes, Ceriodaphnia lacustris 

 Birge, Sida crystallina (O. F. Miiller), Acroperus harpae Baird, 

 Pleuroxus procurvatus Birge, Diaphanosoma brachyurum (Lieven) 



