A FRESHWATER ANAEROBIC CILIATE. 



93 



the anterior third of the organism appears to be filled with minute 

 granules which give this portion a somewhat darker color. The 

 maximum length ranges from 35 p to 40 // and the greatest width 

 from 15 /j. to 17 M- 



This ciliate was found each season from 1914 to 1917 inclusive, 

 but it was most abundant in the former year and scarcest in the 

 latter. The accompanying table shows its vertical distribution 

 in four sets of observations which are typical of the entire series. 

 This table also shows the relation of the organism to temperature, 

 dissolved oxygen, and free carbon dioxide. The observations 

 were made at a regular station where the lake has a depth of 

 23.5 meters. 



TABLE I. 



THIS TABLE SHOWS THE VERTICAL DISTRIBUTION OF THE CILIATE AND ITS 

 RELATION TO TEMPERATURE, DISSOLVED OXYGEN AND FREE CARBON 



DIOXIDE. 



In 1914 regular observations were not begun until the first of 

 September and this ciliate was first noted on September 16. 

 The number rose to a maximum of 95,200 individuals per liter 

 of water at a depth of 16 meters on September 29. From the 

 latter date until October 21 the organism was abundant, but by 

 October 23 the number had decreased 70 per cent., and by October 



