AMICRONUCLEATE RACES OF INFUSORIA 



333 



The graph of the division rate of line Ub which was continued 

 longer than any of the others and accordingly studied most 

 thoroughly is given in figure 2. 



TABLE 1 



In brief, these ten lines throughout their life bred true with 

 respect to the presence or absence of micronuclei — certain lines 

 (Uc, Ue, Uf, Uj) invariably exhibiting large, easily discernible 

 micronuclei, while other lines (Ua, Ub, Ud, Ug, Uh, Ui) consis- 

 tently w^ere without micronuclei (cf. figs. 3 and 4). 



Fig. 2 Graph of the rate of reproduction of an amicronucleate race of Uro- 

 styla grandis. The average daily rate of division of the lines is again averaged 

 for five-day periods. 



Urostyla grandis is not a common hypotrichous form, and the 

 only time I have ever found it at New Haven was in the mass 

 culture mentioned above. Accordingly, it seems probable that 

 all of the animals of the 'w^ild' culture were descended from 

 the same stock and that the separation into a micronucleate 



