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. Inno 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- 
June d to Oct: 1 Oct. 1 to June 1 
| 
| 
Year pala | amphiceros | pala amphiceros 
No. [S$] No |S#) wo [BE] wo. [BE 
et aS 3) lee io 
NSS Bt ad 3 R042. |). 1SSiS 28 6) 863247 —-\ 7 1-1.336;618| 29 
USOC hal one, 14,637 | 14] 89,400 | 86| 958,265 | 87 |144,087| 13 
| | 
SONG ei deecy 14,600 | 4| 3,776,400 | 96 719,650 | 44 |912,580| 66 
1BOS eee, 10,440 | 4] 229,720 | 96 129,623 | 17 |657,960| 83 
Average......| 11,679 |6:5 | 1,062,711 |93.5) 667,696 -| 55 |512,811| 45 
| | | 
