124 



Codonella is an important element in the food of many of the lim- 

 netic rotifers, especially Asplanchna. 



Codonella is a common constituent in the plankton of our own 

 Great Lakes (Smith, '94; Kofoid, '95; Jennings, 'OOa), and has 

 been reported from most European waters. Apstein ('96) finds in 

 German lakes major pulses in spring and autumn and minor ones in 

 midsummer. Lauterborn ('94) reports Codonella in the plankton of 

 the Rhine, and Schorler ('00) in that of the Elbe, but neither follows 

 its seasonal history. 



Coleps hirtus Ehrbg. Average number, 1 3 . This species occurred 

 in the plankton collections irregularly and in small numbers, princi- 

 pally in autumn months during the height of the bacterial develop- 

 ment. It escapes through the silk readily. 



Colpoda cucullus Ehrbg*. Average number, 9,615. This species 

 appears in the plankton principally during the colder months of 

 bacterial predominance, from November to April, and occasionally 

 during the summer. 



Cotkurniopsis vaga (Schrk.) Blochmann was found in both 1898 

 and 1899 on Canthocamptus. 



Didinium nasutum (O. F. Miill.) Stein*. Average number, 

 12,692. This species also is found in the plankton during winter 

 months, especially in November and December during the bacterial 

 increase. It was also found in midsummer. 



Epistylis spp. Average number, 2,020. The free heads or frag- 

 ments of colonies of one, or possibly of several, unidentified species of 

 Epistylis, or it may be of Opercularia also, were associated with Car- 

 chesium lachmanni in the plankton during the colder months, but in 

 much smaller numbers (1 to 13 in 1898). Identification in most cases 

 was impracticable, though in some instances E. flavicans Ehrbg. was 

 determined, and it seems probable that most of the winter forms at 

 least belong to this species. Hempel ('99) reports E. plicatilis on 

 snails, and various other aquatic animals have been found infested 

 with colonies of undetermined species of Epistylis. 



The distribution of Epistylis in the plankton (Table I.) is in its 

 limits somewhat like that of Carchesium. It is more abundant and 

 more continuously present during the period from November to June 

 (at temperatures below 60) than in the intervening warmer months. 

 It is found throughout the whole range of temperatures. Its pulses 

 coincide with those of Carchesium when they occur, but they are not 



