Inheritance of Variations 



81 



investigated from this point of view the infusorian Stylony- 

 chia. Beginning with a single individual, he selected on the 

 one hand the offspring that divided first ; on the other those 

 that divided last. Continuing to select for rapid fission rate 

 in one line, for slow fission rate in another, and keeping this 

 up for hundreds of generations, he found after many gen- 

 erations that there were real inherited differences. Two sets 



Figure 25. The infusorian Stylonychia; diagram to show the differ- 

 ences in time of fission in offspring of the same parent, with the method 

 of selection for rapid fission and slow fission. Constructed on the baws 

 of a figure of Middleton, 1915. 



A, the parent divides into two offspring (B), one of which divides 

 into two while the other still remains undivided (C). Similar condi- 

 tions appear in D and E. Thus in JJ, the large individual at the right 

 is the result of but two divisions from A, while the small individuals 

 to the left are the result of four. 



were produced from among the descendants of a single par- 

 ent, one set that divided more rapidly than the other. 

 The difference persisted for long after selection had stopped. 



Thus it was shown that in this case hereditary diversities 

 are arising, even with respect to a character so readily 

 modified by the environment as is the fission rate. 



This, so far as it goes, of course tends to raise the pre- 

 sumption that other characters of such organisms will be 

 found to show similar hereditary changes when studied with 



