The Distribution in the Upper Meter. 



407 



THE DISTRIBUTION IN THE UPPER METER, AND THE DIURNAL MOVE- 

 MENT. 



Figures 32, 33. 

 The observations recorded in my former paper showed uni- 

 formly that there was no general diurnal movement of the Crus- 

 tacea and no movement at all which could be detected by the 

 use of three-meter intervals. This conclusion has been con- 

 firmed by all of the observations which I have since made. 

 During 1895 and 1896 considerable attention was paid to the 

 distribution of the Crustacea in the upper meter, with the de- 

 sign to determining whether or not there was a diurnal move- 

 ment of the limnetic forms within narrower limits than three 

 meters. A large number of observations were made in 1896 in 

 order to determine the relative number of Crustacea in the upper 

 meter and the remainder of the 3 m. level. These observations 

 were begun early in August and continued until the last of No- 

 vember; twenty sets of observations being made in all. In 

 some cases the Crustacea were taken meter by meter and the 

 numbers compared. In other cases the Crustacea of the upper 

 meter were caught and their numbers compared with those ob- 

 tained from the entire depth. A single illustration of the 

 former method is given; partly in order to show the results, 

 partly also to illustrate the amount of agreement and difference 

 between the three catches of one meter each and that made 

 through the entire distance of three meters. 



Table XXXVI. — Number of Crustacea caught August 24, 1895. 6 P. M. 



Depth, meters. 



0-1 



1-2 



2-3 



Total 



0-3 



Diapto- 

 mus. 



Cyclops. 



D. hyalina. 



D. retro- 

 curva. 



Diaphan- 

 osoma . 



700 

 340 

 460 



36U 

 360 

 370 



2,120 

 2,060 

 1,150 



280 

 200 

 160 



140 

 140 



50 



1,500 

 1,780 



1,090 

 1,050 



5,330 

 4,250 



640 

 475 



330 

 350 



Chydorus , 



As would naturally be expected, the ratio between the C5 

 tacea of the upper meter and those of the entire level varies 



