189 



('99) finds amphiceros in the Oder, where it appears in April and. 

 increases until the end of August or the first of September, when 

 it is the most abundant animal in the plankton. In no one of these 

 instances was the examination so long continued or made at such 

 short intervals as in the case of the exploration of the Illinois. The 

 diversity exhibited in these different waters may be paralleled by 

 the fluctuations from year to year in the Illinois, and from all the 

 data it may be inferred that the organism is probably perennial and 

 polycyclic, the number of pulses depending upon local conditions, 

 primarily of the food supply. 



Brachionus pala var. amphiceros Ehrbg. Average number of 

 females, 17,071; of eggs, 5,103. The numbers were much larger 

 (158,299 and 35,392) in the stable conditions of 1897, and still 

 smaller (5,430 and 715) in the disturbed conditions of 1896. 



The seasonal distribution of this variety with respect to that of 

 the type constitutes the chief point of interest in the records. It is 

 present throughout the whole range of temperatures, shares in the 

 vernal and autumnal pulses noted for the species as a whole, but 

 constitutes a much greater proportion of the amphiceros-pala group 

 during the warmer months than it does in the colder ones. Thus, 

 as shown in the accompanying table, the proportion which amphi- 



SEASONAL DISTRIBUTION OF BRACHIONUS PALA AND B. PALA VAR. AMPHICEROS. 



