The Annual Distribution of the Crustacea, 



405 



Table XXVI. 



1895. 



Total 



Number 



taken. 



July 



August 



September 



285 

 680 

 156 



Per Cent, in each 3m. level. 



0-3m. 



33.3 

 41.0 

 34.0 



3-6. 



34.4 



28.8 

 28.2 



6-9. 



24.6 

 19.5 

 17.3 



9-13. 



7.4 



9.6 



18-15. 



0.3 

 1.9 

 9.6 



15-18. 



0.0 

 0.2 

 1.3 



This table shows that the average agrees very closely with that 

 of the other limnetic Crustacea. During this season a consider- 

 able number of observations were made after nightfall, but 

 neither in 1894, nor in this year was there any evidence of a 

 movement of Leptodora toward the surface at night, as meas- 

 ured by the three meter intervals. The species is nearly, or 

 quite absent from the upper meter or so during the day, but 

 comes to the surface again with the other Crustacea after night- 

 fall. 



In August, 1895, the number caught in the 0-3 m. level, ranged 

 from 1 to 43 individuals; in the 3-6 m. level, from 1 to 33; and 

 in the 6-9 m. level, from to 46. Below this level, of course, few, 

 or no individuals were obtained. With this range of variation, 

 the percentages might easily be altered greatly by a single ob- 

 servation. 



Nauplii. 



Figure 33. 

 The vertical distribution of the nauplii has been very vari- 

 able, as may be seen from the following facts: On July 17th 

 50 per cent, of the very large number taken were caught be- 

 tween 6 and 9 meters and only 7 per cent, in the 0-3 meter 

 level. On the 18th the distribution was substantially the same, 

 while on the 20th 38 per cent, were found between and 3 me. 

 ters, and 31.5 per cent, between 6 and 9, and on the 21st 49 per 

 cent, were found in the upper level and only 19 per cent, be- 

 tween 6 and 9 meters. On the 5 th of August 90 per cent, were 

 found between 6 and 12 meters, and on the 8th 23 per cent, be- 

 tween 9 and 10 meters, and 50 per cent, between 6 and 10. 



