AN AMICRONUCLEATE OXYTRICHA. II 



137 



daily isolations from July 28th to November 18th, and finally died 

 in the one hundred and second generation, outliving the 'normal' 

 culture (A) by several days. The graph showing the average 

 division rate of the four lines for five-day periods has been plotted 

 together with that of culture A. 



Figure 6 show^s at a glance absolute and relative division rates 

 of the parent culture (A) and its twin derivative (AT). It is 



Fig. 6 Comparison of normal culture, A (continuous line), and twin culture, 

 AT (broken line). Culture AT begins July 28, 1917. Culture A died out on 

 November 17, 1917. The death of culture AT occurred during the next five day 

 period (not shown in figure). 



apparent that the average division rates of A (after AT arose, 

 July 27, 1917) and AT are essentially the same; the various fluc- 

 tuations might well represent those of two cultures of normal 

 animals from the same ancestor. The twin culture outlived the 

 culture of 'normal' animals for a few days, and finally the last 

 representative of culture AT died in the one-hundred-and-second 

 generation. During the last week of the life of the twin culture 



