213 



September. Apstein ('96) finds that this species (including 5. 

 tremula and 5. grandis] is one of the most abundant in lakes near 

 Plon, with variable maxima in different bodies of water. He finds 

 it perennial in one case, and reports vernal maxima. Winter eggs 

 were found in March and April. 



Synch&ta stylata Wierz. Average number of individuals, 120,391 ; 

 of eggs, 17,797. In 1897, 42,577 and 9,127; in 1896, 24,099 and 

 5,125; in 1895, 155,880 and 2,418; in 1894, 8,582 and 132. This 

 species affords an exception to the general rule hitherto observed 

 among the rotifers of our plankton in that it is more abundant in 

 1898 than in the previous year. As will be seen in the following 

 table both the vernal and autumnal pulses are unusually large in 

 1898, while in the previous year the vernal pulse is only moderate 

 and the autumnal pulse is scarcely to be detected. For some 

 reason the prolonged low water and sewage contamination of the 

 autumn of 1897 was not favorable to the usual grow r th of this 

 species. It may be that it was crowded out by the unusual develop- 

 ment of Polyarthra at that season (PL V.). 



PULSES OF SYNCH^ETA STYLATA. 



