—e 
229 
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.’, May—JuNE, 1898. 







Date Females ees Young Total living | Dead 
AG 800 0 0 s00.—s| 0 
Maye a3 sacs ne ss 1,600 400 800 2,800 O 
eee Oger 3 1,600 1,000 1,000 | 3,600 400 
aL fatacsy Sonic 37 1,300 1,100 1,100 3500 | 100 
ee Ae ee es, .3,280 1,400 1,240 5,920 920 
Re TLC ater cliche 25,120 2 ,000 6, 800 33,920 | 1,280 
[CMe Woecomac 38,800 9,200 14,800 62,800 9,200 
seam Ar a) 3,24, 2,200 3,000 800 6,000 1,400 
OO PAS ee 1,000 500 O | 1,500 | 100 
eS him cess 300 } 200 200 | 700 | 100 


Bosmzina 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 
