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part in the seasonal delimitation of the amplitude of Bosmina pulses. 

 The Bosmina population in the plankton consists largely of 

 parthenogenetic females. Males and females with ephippial eggs, 

 were recorded only in October-December, 1897, and then only in 

 small numbers and isolated occurrences. Females with eggs or 

 embryos and the free young were found at all seasons of the year and 

 at all temperatures, but most abundantly at the time of the pulses. 

 Parasitized or fungused individuals are also found occasionally at 

 these seasons of greatest numbers, and the high mortality following 

 a pulse is evidenced by the large number of dead occurring in the 

 plankton. The proportions of females, females with eggs or em- 

 bryos, young, and* dead during the May- June pulse of 1898, may 

 be traced in the following records. 



BOSMINA PER M. 3 , MAY-JUNE, 1898. 



Bosmina longirostris has been frequently reported in the plankton 

 of European lakes. Apstein ('96) finds it perennial in Plonersee 

 with larger numbers in June-September and a maximum in July. 

 No pulse-like recurrence is noted, parthenogenesis prevails, and 

 males and ephippia are rare. His results, save in the matter of 

 pulses, are thus in general accord with ours. Stingelin ('97) notes 



