238 



and fungused individuals were also noted in these periods of decline. 

 Males were recorded in September, December, and February. 



Chydorus is not given as a constituent of the plankton of Nor- 

 wegian lakes by Huitfeldt-Kaas ( '98) or of Swiss lakes by Fuhrmann 

 ('00), Amberg ('00), or Burckhardt ('00 and 'OOa). Its absence 

 from these cooler waters stands in sharp contrast with its abundance 

 in warm and shallow European lakes. It is reported as abundant 

 in Chroococcacea-rich lakes of North Germany by Apstein ('96), 

 where it is acyclic, with larger development in April-October, and 

 maximum in August or in May- June. According to Weismann 

 (79) Chydorus in some waters is polycyclic. It is also reported by 

 Zacharias ('97a and '98b) from the pond fauna of Trachenberg and 

 many other German localities, where it forms '"em notorisches 



