17 per liter in the latter part of the month. It declined to 11 

 per liter in early July, but soon began to increase, reaching the 

 season's maximum of 3U per liter in early August. By late August 

 the number had decreased to l6 per liter, and it continued to 

 decrease to 7 per liter in the early days of October. Cyclops thus 

 had two periods of abundance, a minor one in late June, and a period 

 of great abundance in early August. The first period of abundance 

 coincided with the second of Diaptomus; the second came when 

 Diaptomus was declining toward the season's minimum, 



Daphnia first appeared in the quantitative samples in 

 early May, It increased rather rapidly and uniformly to the maximum 

 of 10 per liter in late June. During July it decreased, reaching 

 a low count of 2 per liter in the latter half of the month. In 

 early August it increased again to U per liter and remained almost 

 uniform until the decline of early October, The increase of early 

 August over late July is so small that there is some question whether 

 it should be regarded as a real increase. This point will be referred 

 to when the two years are compared. 



The nauplii were rather rare in early April but increased 

 rapidly during the month, and continued to increase to the season's 

 maximum of 37 per liter in early May. By late May they had decreased 

 to 21 per liter, but in early June the count recovered to 26 per 

 liter. Thereafter the nauplii declined, with minor halts, to the 

 minimum in late September and early October, 



Diaphanosoma appeared in traces in May but was not a regular 

 constituent of the plankton until late June. The time of maximum 

 abundance was early August when there were 6 per liter. During the 

 remainder of the season the count was lower by one half or more, 



Limnocalanus was present in the earliest samples and 

 remained in small numbers through early July. It was most alxindant in 

 May, but never reached a count of 1 per liter, Epischura first ap- 

 peared in early May and disappeared from the trap samples in early 

 August, It was quite rare throughout its season, never becoming as 

 abundant as 1 per liter. Bosmina appeared in late April at one 

 station and attained some abundance throughout the section during May 

 and June, It disappeared during July, but returned in August and re- 

 mained for the balance of the season. The highest count recorded 

 was l5 per liter at Station 59A in late June; the average for the 

 section at this time was Ii per liter, and it was about equally 



222 



