94 CHANCEY JUDAY. 



27 it had entirely disappeared. The autumnal overturn took 

 place between the last two dates, with the consequent aeration 

 of the water at all depths, and this event was followed by the 

 prompt disappearance of the ciliate. 



In 1915 this organism was found in small numbers in four 

 sets of observations between July 12 and July 22. The stratum 

 of water which it occupied at this time contained from o.io c.c. 

 to 0.40 c.c. of dissolved oxygen per liter. Following the latter 

 date it was not found again until August 19 and August 23 when 

 a small number was noted in a stratum of water which contained 

 no dissolved oxygen. It appeared regularly in catches made 

 during September, the largest number being found during the 

 latter part of this month. It disappeared between September 

 29 and October 6, the autumnal overturn and aeration of the 

 lower water having taken place in the meantime. 



In 1916 this ciliate was noted twice in July, but it did not 

 appear again until September 18, when it was obtained during 

 the following ten days. In 1917 it was found only in September 

 and then only in small numbers. 



This protozoan showed a downward movement each autumn 

 which was correlated with the descent of the thermocline or 

 mesolimnion, the organism keeping just below the stratum of 

 aerated water. Thus in the table above it will be noted that 

 the stratum occupied on October 21, 1914, was three meters 

 deeper than that of October 10. This descent continued until 

 the bottom was reached and then the ciliate disappeared promptly, 

 usually within two days, after the bottom water became aerated. 

 In the laboratory it lived in water that had been partially aerated 

 only for a period of about twenty-four hours. 



As indicated in the table there did not seem to be any corre- 

 lation between the vertical distribution of this ciliate and the 

 temperature of the water or the amount of free carbon dioxide, 

 but there was a definite correlation with the lack of dissolved 

 oxygen, the stratum occupied having at the most only a minimal 

 amount of this gas and most frequently none at all. This fact 

 and the further fact that it disappeared so promptly when the 

 water became well aerated seem to warrant the conclusion that 

 it is substantially an anaerobic ciliate. 



