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, 00a), 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, 13. 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. 
Cothurmopsts vaga (Schrk.) Blochmann was found in both 1898 
and 1899 on Canthocamptus. 
Didinium nasutum (O. F. Mull.) 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 
Epistylts, or it may be of Opercularta 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 EF. flavicans Ehrbg. was 
determined, and it seems probable that most of the winter forms at 
least belong to this species. Hempel (99) reports FE. plicatilis on 
snails, and various other aquatic animals have been found infested 
with colonies of undetermined species of Epistylis. 
The distribution of Epzstylis in the plankton (Table I.) is in its 
limits somewhat like that of Carchestum. 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 Carchesiwm when thev occur, but they are not 
