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. I have 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. 



Brachionus pala var. dorcas has not been found widely distributed 

 in the fresh- water plankton, or at least not reported separately 

 from B. pala, which is widely distributed. Skorikow ( '96) reports 

 it from Charkow, Russia; and Kertesz ('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 spinosus 100,044 on April 24, 

 1896 w r as 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, 



