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THE AMEBIC AN NATURALIST [Vol. XLIX 



Seasonal Variation.— In the autumn and early winter 

 Vaucheria was usually present, but appeared only twice 

 in the spring. Pandorina and Peridinium also appeared 

 late in the year. At that time fewer protozoa were seen 

 than in the spring, but, as has been said, variations here 

 seem to be more closely related to the character of the 

 water than to the temperature. Gammarus and the 

 nymphs of may-flies and dragon-flies were most numer- 

 ous in October, November and December. 



The spring season also had its special forms. Oscil- 

 latoria appeared first in March and was constant there- 

 after. Diatom production was at its height in April and 

 May at water-temperatures varying between 8° and 16° 

 C. and there was a marked decline in diatom appearances 

 toward the end of June. In contrast to diatoms, desmids 

 seem to require higher temperatures, since most of the 

 Closterium and all of the Cosmarium and Staurastnm 

 that were seen appeared in June, in water at temperatures 

 between 15° and 20° C. The proportion of Dinobryon 

 in collections became noticeably greater during the latter 

 part of June. The smaller crustaceans, excepting the 

 ever-present Cyclops, showed marked increase in num- 

 bers as well as in diversity during May and June. The 

 same seasonal increase was noticed for Anguillula and 

 the rotifers. Most of the coleopterous and dipterous 

 larvae were found in May and June, except Chironomus 

 which was present at all seasons. 



Another point of interest in connection with seasons is 

 the time of reproduction. Spirogyra was found conju- 

 gating in October, April and June; Mougeotia in Novem- 

 ber, December, May and June. Young, sessile plants of 

 XJlothrix were seen in April and May. All through the 

 year, copepod nauplii and female Cyclops bearing egg- 

 sacs were observed. Chironomus eggs were found in 

 April and early in June, while very young larvse were 

 abundant during April, May and June. 



In view of the fact that floating alga- were found in 

 large quantities in December, even under ice, it was sur- 



