A FRESHWATER ANAEROBIC CILIATE. 



CHANCEY JUDAY. 



Investigations on a considerable number of Wisconsin lakes 

 have shown that, in many of them, more or less of the lower 

 stratum, or hypolimnion, and the muddy ooze at the bottom 

 possess no free oxygen for a certain time during the summer 

 stagnation period (Birge and Juday, 'n). This time varies 

 from three or four weeks in some lakes to as many months in 

 others. The dissolved oxygen disappears gradually from this 

 stratum as the season advances and when it reaches a minimal 

 amount the various organisms occupying this region respond to 

 the change either by migrating or by adapting themselves to the 

 new conditions. 



When the minimum is reached for plankton Crustacea they 

 rise to a higher level where oxygen is more abundant and when 

 this gas becomes too scarce for some of the bottom dwelling insect 

 larvae they migrate to the shallower water. The majority of 

 the forms, however, are able to remain here even in the absence 

 of free oxygen. To this latter group belong representatives of 

 at least seventeen genera of protozoa, including rhizopods, 

 flagellates and ciliates, but chiefly ciliates, and a number of 

 higher forms, such as insect larvae, an ostracod, worms, and a 

 bivalve mollusk. These forms appear to thrive as well in water 

 which contains no free oxygen as in water which is well aerated, 

 thus being facultative anaerobes (Juday, '08). 



While making a study of the centrifuge plankton of Lake 

 Mendota a ciliate was found in the lower stratum of water which 

 appears to have gone beyond the facultative stage so that it has 

 become substantially a true anaerobe. This ciliate agrees very 

 closely in shape and structure with Fig. 126, Plate X., of Conn's 

 "Protozoa of the Fresh Waters of Connecticut," which this author 

 "with hesitation" places provisionally in the genus Enchelys. 

 It has uniform ciliation, a rather pointed, obliquely truncate 

 anterior end, and a rounded posterior extremity. Frequently 



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