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. 3 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 1 6 ; once 

 on the decline of that of October 2 5 ; and once on that of December 1 5 . 

 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. 



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. 



