ENDOMIXIS IN PARAMECIUM AURELIA. 439 



aquaria, ponds, etc., and, of course, thoroughly boiled and 

 allowed to attain room temperature before being used. Some 

 of the subcultures directly involved in the experiments have 

 been bred on this medium. Others have been bred on the beef- 

 extract medium which we have employed in other work on 

 Paramecium, 1 or on other media which will be described in con- 

 nection with the individual experiments. 



The subcultures which have been the basis of the present 

 work may be tabulated as follows : 



SUBCULTURES. 



A (from Main Culture I) Oct. 15, 1914, to Feb. 12, 1916. (485 days.) 



4675th to 5592d generations. 

 AE (from IE) 2 Oct. 15, 1914 to Aug. 12, 1915. (Twice restarted during the 300 



days.) 



4637111 to 5079th generations. 

 O (from III) Oct. 15, 1914 to Nov. 20, 1915. (Once restarted during the 400 



days.) 



I7th to 775th generations. 

 B (from IV) Jan. 8, 1915 to Jan. 14, 1916. (372 days.) 



3d to 6o9th generations. 

 M (from V) July 17, 1915 to Feb. 23, 1916. (222 days.) 



3d to 550th generations. 



W (from VI) Aug. 12, 1915 to Jan. 14, 1916. (152 days.) 

 3d to 302 d generations. 



The data are presented chiefly by graphs of the division rate 

 of the various subcultures. These are plotted by averaging 

 the daily rate of division of the several lines of the respective 

 subcultures and then again averaging this for five-day periods. 

 The figures I, 2, 3 represent divisions and 10, 20, etc., indicate 

 the number of the five-day periods. An E shows that endomixis 

 was observed during the five-day period. Inclusion of a part 

 of the curve within brackets indicates that the cells were not 

 studied cytologically during this time. Cf. Figs. I and 7. 

 Since so much depends on these graphs and the five-day periods 

 which they comprise it may be well to repeat a statement made 

 in a previous paper: 3 



1 Woodruff and Baitsell, "The Reproduction of Paramecium aurelia in a 

 'Constant' Culture Medium of Beef Extract," Journ. Exper. Zool., XL, i, 1911. 

 * IE is a subculture isolated from Main Culture I. in October, 1913. 

 3 Woodruff and Erdmann, Journ. Exper. Zool., 1914, p. 477. 



