626 Lorande Loss Woodruff. 



that this had a very insignificant influence on the fission-rate is 

 shown by the accompanying table. The experiment certainly 

 substantiates Maupas's result, however obtained, that light is of 

 little or no direct importance in the economy of the ciliate. 



Oxytricha A (light) 



Oxytricha A' (darkness) 



A -I 23 divisions. 



A -2 28 " 



A -3 17 " 



A -4 20 " 



Total, 88 divisions. 



A^-i 22 divisions. 



Ai-2 26 « 



A*-3 16 " 



A>-4 18 « 



Total, 82 divisions. 



Excess in light, 6 divisions. 



VIII. SUMMARY. 



1. The chief object of the work was to ascertain if the life- 

 history of hypotrichous Infusoria is characterized by "cycles," 

 and if so, the cytological changes which occur and the effect pro- 

 duced on the cycles by changes in environment. 



2. Two cultures of Oxytricha fallax, two of Pleurotricha lan- 

 ceolata, and one of Gastrostyla steinii have been carried on. 

 Oxytricha culture A extended from October 26, 1901, to July 14, 



1903, during which time 860 generations were attained. Culture 

 B was started December 10, 1902, and died out through an acci- 

 dent November 22, 1903. Pleurotricha culture A was isolated 

 November 10, 1902, and became extinct July 3, 1903. Culture 

 B was carried continuously from November 25, 1902, to March 13, 



1904, when it was lost by an accident. The culture of Gastrostyla 

 was started May 28, 1904, and died out December 5, 1904. The 

 life-history of each culture is represented graphically by a curve 

 which is plotted by averaging the number of divisions per day of 

 the four lines constituting each culture, and then averaging this 

 for five- or ten-day periods. 



3. All the cultures give incontestable proof that the species 

 studied pass through periods of greater and less general vitality 



