148 



J. A. DAWSON 



Series VIII . A twin was isolated on February 9, 1918, from 

 a Petri-dish culture of stock animals from subculture A4C, 

 line 3, which was begun January 30, 1918. As usual there were 

 present in the culture a considerable number of pairs as well as 

 several cannibals. 



Records of the division rate of this series were kept until 

 March 11, 1918, when they were discontinued, the twins being 

 then in the twenty-fourth generation and the single animals in 

 the twenty-sixth. The cultures are at the date of writing still 



1 ==:== 



Figure 13 



Figure 14 



Fig. 13 Comparison of twin culture (S8T, continuous line) and of subculture 

 of single animals (S8TS, broken line) derived from the twin culture. February 

 14 to March 11, 1918. 



Fig. 14 Comparison of twin culture (S9T, continuous line) and of subculture 

 of single animals (S9TS, broken line) derived from the twin culture, February 14 

 to March 13, 1918. 



living and dividing. Essentially the same story is told by the 

 curves for this series as in the others. 



Series IX. The twin ancestor of series IX was obtained Feb- 

 ruary 9, 1918, from a depression-slide culture from stock animals 

 of line 3 culture A3N, begun February 2, 1918. The second 

 generation gave one twin and two single animals, both of which 

 died the following day. The twin divided to give two twins, 

 both of which in the next generation gave one twin and two 

 single. 



