278 



the warmer season, on the other hand, the pulses frequently attain 

 100,000 or over. 



The maximum record of 928,984 was made in the stable low 

 water of June 19, 1895. All large developments thus lie at tem- 

 peratures above 70. 



The nauplii bear much the same relation to hydrographic condi- 

 tions as that found in the adults; for example, in Cyclops viridis. 

 This is seen in the fact that in unstable years such as 1896 and 1898 

 the numbers are on the average only 28 and 68 per cent, of what 

 they were in the more stable conditions of 1895 and 1897, and the 

 average monthly population in July-December in the unstable 

 conditions of 1898 is only 18 per cent, of that in the same months 

 of the previous year. 



The relative numbers of adult, young, and larval stages of the 

 Cydopida are given in the accompanying table. 



The ratios between total adult and young, 1 to 5, are fairly 

 constant in the different years, falling to 1 to 3 in January-March, 

 1899, and to 1 to 4 in 1898, a year in which the colder part of the 

 year was most fully represented. This ratio probably represents 

 more truly the relationship of young and adult in the total yearly 

 production. The ratios of adults to nauplii in the several years 

 vary considerably from the totals of all years (1 to 21), rising to 1 to 



