268 
water were not infrequently found. In a few instances, owing 
to roughness and rottenness of the ice, it was not possible to 
reach the point up-stream where the collections were usually 
made, and in such instances the catch was taken nearer Ha- 
vana but always above the mouth of Spoon River (Pl. I.). Even 
when the ice was running at the time of break-up, it was 
possible by floating in rifts of the floes to secure a catch of 
the channel plankton. Thus in all seasons our catches at this 
station are typical of the channel plankton. 
CHRONOLOGY OF COLLECTIONS. 
As shown in Table IIL., the collections at this station cover 
the period from June 12, 1894, to March 28, 1899, in which 
time catches were made on 235 different days, 10, 50, 76, 34, 
52, and 13, respectively, for the several years included. The 
interval between collections in 1894 (Pl. VIII.) ranges from 14 
to 34 days. In the first half of 1895 (Pl. IX.) they were few 
and irregular, but four being taken, while in the second half of 
that year 46 were taken at intervals of one to twelve days, the 
interval varying with flood conditions, since an attempt was 
made to follow closely the effect of changing river levels upon 
the quantity of plankton. The December flood of this year 
was followed at intervals not exceeding five days until Februa- 
ry 10 of the following year (Pl. X.). From this time till April 
24 the intervals average about seven days, in no case, however, 
exceeding eleven. From this date till the end of August, 49 col- 
lections were made at intervals of one to seven days, following 
thus closely the fluctuations attendant upon the two recurrent 
floods of that season (Pl. X.). The field station at Havana was 
then closed, and until it was reopened in the following July 
fortnightly or monthly trips were made to Havana for collec- 
tions (Pl. XI.). From this time until the suspension of opera- 
tions March 28, 1899, the collections—with the exception of a 
few extras and two delays due to sickness—were made at regu- 
lar weekly intervals (Pl. XII., XIII.). Thus, in one or another 
of the years in question all months but October, November, 
