General Distribution of the Crustacea. 439 



the Crustacea could be traced to these varying conditions of the 

 weather. It is worth noticing that the number of Crustacea 

 obtained was not to any notable extent affected by the direction 

 of the wind. Since our buoy was placed about -J of the distance 

 across the lake, it might reasonably have been expected that 

 the pelagic Crustacea would be decreased in number by a breeze 

 blowing from the nearer shore, and possibly somewhat increased 

 by a wind from the farther shore. No such effect, however, was 

 observable and indeed the number of Crustacea obtained in the 

 last period, when the wind was from the more distant shore, 

 was smaller in all species than the number obtained in the pre- 

 ceding series, when the wind was from the nearer shore. 



GENERAL DISTRIBUTION OF THE CRUSTACEA. 



Altogether 59 sets of observations were counted, and are 

 made use of in determining the average of the distribution ot 

 Crustacea for the month. The number of observations varies 

 somewhat in the different levels. Forty-nine observations only are 

 recorded for the lowest level, 15-18 m. , for reasons indicated 

 above. In each of the upper levels, except the upper, from one 

 to three observations were lost by various accidents. In one or 

 two cases the dredge did not open or close properly, thus vitiat- 

 ing the observation. In one or two cases the contents of the 

 dredge were partially lost, thus making it impossible to count 

 them. However, the general uniformity of observations is such 

 that no noteworthy change would be made in the results if all 

 the sets of observations had been perfect. In the last three 

 periods observations were taken at intervals of three hours dur- 

 ing the day and night. The times selected were midnight, 3 

 a. m. , 6 a. m. , etc. The observations taken at 9 p. m., mid- 

 night, and 3 a. m. are reckoned as belonging to the night. 

 Those at the other hours are reckoned as belonging to the day. 

 In July, of course, the hours of 6 a. m. and 6 p. m. are fully 

 within the daylight hours. Had there been any diurnal move- 

 ment of the Crustacea these observations would have been 

 treated by themselves, but since the day observations do not 

 differ in any marked way from those made at night, the 6 a. m. 

 and 6 p. m. series are included and averaged with those of the 



