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 (PI. 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 III., 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 (PI. VIII.) ranges from 14 

 to 34 days. In the first half of 1895 (PI. 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 (PI. 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 (PI. XL). 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., XIIL). Thus, in one or another 

 of the years in question all months but October, November, 



