GENERAL CONSIDERATIONS 



29 



motile organs may be lost (Maupas, ibid.). In U role plus mohilis the 

 chromatin of the macronucleus ultimately disappears and only a few 

 X-granules remain. The protoplasm apparently dies from "old age" 



(Fig- 9). 



The effects of continued division in ciliates, if other means of re- 

 organization are excluded, are clearly shown by the method of isolation 



Figure 9. Uroleptus mobilis Engelm. Old-age specimens showing the degeneration 

 of the macronucleus (M) and loss of micronuclei. (After Calkins, 1919.) 



cultures. A single individual, preferably an ex-conjugant, is isolated 

 in a suitable medium in a culture dish such as a Columbia isolation cul- 

 ture dish. The next day such an individual, for example a U . mobilis, is 

 represented by four or eight daughter individuals, the number depending 

 upon two or three divisions of the original one isolated. In our practice 

 five of these are isolated in separate dishes, and five independent 

 lines are started, all representing protoplasm which had been a part 

 of the protoplasm of the original individual isolated. A single individual 

 is isolated daily from each of these five lines and a daily record of 



