10 



THE AMERICAN NATURALIST [Vol.LVI 



too has obsorvod a fow cases in which strains of Parame- 

 cium became differentiated in ways that could hardly be 

 considered the result of environmental action. Doubtless 

 some other cases might be collected. Here then we seem 

 to lia\'e what wo were searching for; here at last is some- 

 thing solid; here by our presuppositions we have evolu- 

 tion evolving; we have seen it! But as with so many of 

 the seeming solid things of science — .so these became 

 sicklied o'er with a pale cast of thought, of doubt, of 

 speculation. What, it is asked, is the cause, the funda- 

 iiiciital nature, of these persistent changes? And are 

 liicy indeed of a sort to be considered steps in evolution? 



And when we look closely, the observational and selee- 

 tional work has given us little infonnation on these 

 points. Tn ArceJIa liegner found that certain of the in- 

 herited structural changes are mere results of increase or 

 decrease in number of iiuclei, l)roug]it a})()ut in a simi)le 

 manner. But most of the changes in the lower organisms 

 studied can not be accounted for in this way. The work 

 of Erdmann (1920) indicates that certain jiersistent 

 changes occui" in Paraiiicciit ni as a result of the jjeriodic 



IS a favorite sp. cnl.'U i\ i.lr;i with opposing speculators 

 that most or all of ihr pcr-isting changes we have men- 

 tioned arise thnumh iri-.-nlarities in nuclear division, 

 and hence are of litth" evolutionary significance, but this 

 is thus far a mere possibility, without solid base; as the 

 (iermans say, it floats in the air. Another s])ecuhUive 

 notion is that tlie ciian-es lack Drnnanenc.^ : tlo.i if i'nl. 



would 

 of the 



It 



