Distribution of Cyclops. 461 



was at 3 m. almost exactly. In Periods III and IV it was 

 between 3.9 m. and 4 m. 



Horizontal distribution of Diaptomus and Cyclops. — On July 

 23 and 31 two series of observations were taken in the — 3 m. 

 level at widely separated parts of the lake, in order to get some 

 idea of the horizontal distribution of the Crustacea. The num- 

 ber of Cyclops and Diaptomus in these catches was determined, 

 with the following result: 



July 23. 



Diaptomus 3600 4210 3280 3320 3240 2620 



Cyclops 1060 2620 2550 1760 3690 2330 



July 31. 



Diaptomus 2320 1750 1860 1190 3870 



Cyclops .. 1300 1490 1110 900 1010 



These numbers vary in much the same way as do the succes- 

 sive observations made at the buoy both as to actual numbers 

 and in the relative numbers of the two genera, and it is there- 

 fore probable that the place selected for our observations fairly 

 represents the average conditions of the lake. Two successive 

 observations were taken at the buoy at this time with the fol- 

 lowing result: 



Diaptomus 2100 2440 



Cyclops 1256 1250 



These results show an agreement quite as close as could be 

 expected. The numbers are larger than the average, especially 

 those of Cyclops. 



