The Annual Distribution of the Crustacea. 



313 



ing the same months, those individual of Daphnia retrocurva 

 disappear, which have survived the reproductive period. Diap- 

 tomus begins its decline in September or early October, and 

 seems to make no special provision for winter forms. Cyclops 

 continues its reproductive activity through the year, at least in 

 periods when the temperature of the lake is above 2° C, but 

 with a rate of multiplication declining as the temperature falls 

 below 15°. Larval Copepods are present in great numbers at 

 all seasons, but their development into later stages is checked in 

 winter. Chydorus seems to have the same habit as Cyclops; but, 

 for causes as yet unknown, it almost disappeared in the winters 

 of 1894-5, 1896-7^ although abundant in the preceding autumns, 

 and present in considerable numbers in the winter of 1895-6. 

 Daphnia pulicaria had a marked reproductive period in early 

 December, and continued reproduction at a slower rate through- 

 out the winter. Diaphanosoma disappears in October, and 

 Leptodora in late November or early December. 



Table IV. — Average number of Crustacea for each two-week period and 

 their sum, stated in thousands and tenths per sq. meter of surface. 





Diap- 

 tomus. 



Cy- 

 clops. 



D. puli- 

 caria. 



D. hya- 

 lina. 



D. 



retro- 

 curva. 



Chy- 

 dorus. 



Diap- 

 hano- 

 soma. 



Total. 



1894. 



July 1-15 



242.2 

 398.9 



218.7 

 87.4 



39.8 

 151.0 

 161.0 

 200.3 



6.4 

 8.3 

 1.1 



0.8 



19.8 

 13.3 

 16.6 

 60.7 



a 

 a 

 a 

 a 



a 



a 



a 



15.0 



a 



0.8 

 6.3 



18.0 



306.2 



July 16-31 



472.3 





401.1 



August 16-31 



382.2 







September 16-30 



October 1-15 



54.6 

 67.6 

 38.3 

 44.0 



190.1 

 347.1 



261.3 

 216.4 



a 

 a 

 a 

 a 



148.4 



207.6 



253.5 



183.1 



a 

 a 

 a 

 a 



278.9 



193.3 



202.0 



97.9 



19.6 

 5.2 

 3.0 

 a 



691.6 

 820.8 



October 16-31 



757.1 



November 1-15 



571.4 







December 1-15 



23.9 



(16.7J 



17.5 

 (15.9) 

 (44.5) 



75.0 



(44.5) 



21.5 

 (40.0) 

 (80.8) 



a 

 a 



a 

 a 

 a 



121.5 

 (49.0) 



40.8 

 (55.9) 

 (75.3) 



a 

 a 



a 

 a 

 a 



9.5 

 (1.65) 



1.3 



(2.0) 

 a 



a 

 a 



a 

 a 

 a 



219.9 



December 16-31 



(111.9) 



1895. 



January 1-15 



Sl.l 



January 1-15 



(111.8) 





(200. 6> 



