Cyclops. 329 



May 2d to 9th in 1896. The entire month may be included in 

 the maximum in 1895, as all the catches made between May 3d 

 and June 6th, 26 in number, were between 636,000 and 1,234,000 

 per sq. m. In 1896 the limits of the maximum period may be 

 set at April 14th and May 20th, during which time the numbers 

 ranged from 763,000 to 2,359,000 per sq. m. The observations 

 were 20 in number. The maximum catch recorded was nearly one- 

 third larger than any other, although there were 7 catches 

 made, ranging from 1,300,000 to 1,700,000 per sq. m. 



From these figures and from the averages, it is plain that the 

 numbers were far greater in 1896 than in the former year. I 

 attribute the difference to the earlier start which the species 

 had in 1896. In that j^ear reproduction began under the ice so 

 that the numbers at the opening of the season were three or 

 more times as great as in 1895. While the lake warmed some- 

 what more rapidly in 1896, the difference was chiefly marked by 

 the higher temperature of the lower water, which would aid the 

 development of the species during the first part of April. 



The decline of Cyclops is seen from Table XI and diagram 15, to 

 be as steady and rapid as its rise. In 1896 the numbers in the 

 first half of June were smaller than in the latter part of March. 

 In less than two weeks after the maximum the number had fallen 

 to less than one-sixth of the maximum and a week later it was 

 less than one-half of the smaller sum. 



This decline is doubtless due to the scarcity of food, to the 

 increasing temperature of the water and, to increasing competi- 

 tion. At no time during the spring rise are as many as five per 

 cent, of the species provided with egg-sacs and almost none of 

 the animals in the lower strata of the water become sexually 

 mature. This fact indicates that the lake becomes so crowded 

 with the early swarms of the species that the food is insufficient 

 to allow their development to maturity. Not only so, but those 

 individuals which are compelled to migrate into the deeper 

 water find there little food and must perish in a short time. 

 At the height of the Cyclops period there is very little alga 

 visible in the catch. 



The influence of temperature is shown by the fact that the 

 maximum is reached when the temperature of the lake is about 



