191 



















Owing to the ease with which such eggs are detached, the records 
are quite imperfect indices of the actual numbers. In 1898 male 
eggs (carried) to the number of 70,400 per m.? attended the culmina- 
tion of the vernal pulse (419,200) on May 3. Winter eggs (carried) 
were recorded twice on the decline of the pulse of August 16; once 
on the decline of that of October 25 ; andonce on that of December 15. 
Brachionus pala var. dorcas Gosse.—The seasonal distribution 
of this variety is so sharply defined that it merits especial attention. 
The following table gives the dates and temperatures of last and 
first records in each year. 
SEASONAL LIMITS OF BRACHIONUS PALA VAR. DORCAS. 








Last records First records | Largest pulses 
Year i : 
Date Temp. Date | Temp. Date Temp. | No. 
Apr. 29 64° | Oct. 15 | 57° | Apr. 29 64° | 9,000 
Nov. 14 46° 
May 1 202" >| Now 7 |) 44° | Apr. 24 72° | 183,000 
Apr. 27 60° Oct. 12 65° INDI 2h C02. | 2,400 
Jan 11°98 | “32° | 
Apr. 26 57° | Dec. 6 34° | Apr. 26 S724 | * 4.000 
May 17 64° | 




The species practically disappears at the end of April, when 
temperatures rise above 70°, and it does not return to the plankton 
until they fall, in October and November. Its period of continuous 
occurrence does not begin in years of greatest numbers until tem- 
peratures reach 45°, and it remains throughout the period of mini- 
mum temperatures. As the collection-averages indicate, this 
species is relatively rare, and its numbers, even in its largest pulses, 
are usually smaller than those of the other varieties which it accom- 
panies. Although this species is a winter planktont it reaches its 
greatest development during the spring pulse, indicating an opti- 
mum near 65°, though it does not recur in numbers when this 
temperature returns in autumn. There is a single autumnal pulse 
in 1895 of 8,625, on November 14, at 44°, accompanying pulses in 
the other varieties. There was also one midsummer record. 
