192 
The curvature of the median anterior horns which defines this 
variety results in a considerable elongation of these processes. With 
regard to the idea of Wesenberg-Lund (’00) that this tendency on 
the part of plankton organisms to elongate in “ Balanceapparat”’ is 
an adaptation to the lessened buoyancy of the warmer water of 
summer, it must be said that it seems difficult to apply this hypothesis 
in the case of B. pala var. dorcas, which is probably a seasonal variety 
confined to winter months. Ihave no data, however, on the relative 
development of these processes in B. pala at different temperatures, 
beyond the seasonal limitation of this variety to lower temperatures 
when it should be least expected according to the hypothesis. 
Brachonus pala var. dorcas has not been found widely distributed 
in the fresh-water plankton, or at least not reported separately 
from 6. pala, which is widely distributed. Skorikow (’96) reports 
it from Charkow, Russia; and Kertész (94), in January from 
Budapest. 
Brachionus pala var. dorcas forma spinosus Wierz.—Average 
number of females, 33; of eggs, 2. This form was always sporadic 
in its appearance in our plankton. Of 12 occurrences, 3 were in 
April, 2 each in November, December, and July, and one each in 
January, May, and August. The whole seasonal range of tempera- 
tures is thus included. It may be of significance for Wesenberg- 
Lund’s hypothesis that the spinous form of dorcas makes over 50 
per cent. of its appearances between April 1 and September 30, 
whereas dorcas itself is much less abundant relatively within these 
limits. The largest occurrence of spznosus—100,044 on April 24, 
1896—was marked by the fact that 97.5 per cent. of the individuals 
were infested with fungi. The nearest approaches to pulses in this 
form are the November-—December appearances in 1895 and 1896. 
Females with winter eggs were recorded December 29 in the latter 
year. 
Brachionus quadratus Rousselet.—Individuals corresponding to 
Rousselet’s description have been found occasionally in the plankton 
from the last of May till the middle of August at temperatures of 
70° and above. The species is somewhat closely related to the 
bakeri series, and may ultimately prove to belong to it. Rousselet 
(’97) is of the opinion that it is distinct by reason of the truncate 
posterior end, the absence of foot sheath, the reticulations of the 
shell, and the semi-jointed foot. It occurred only in small numbers, 
