134 GENETIC VARIATIONS 



pearance of the macronucleus. Finally, after severe and long- 

 continued action, the environmental conditions alter the 

 reserve genie materials in the micronucleus. Such modifica- 

 tions last either until new^ environmental conditions again 

 alter the micronucleus; or until through conjugation a new- 

 combination of genie substances is made that yields new^ 

 characteristics. 



A final test of whether these intense modifications do in- 

 deed affect the micronucleus must come through crossing a 

 deeply modified stock with one that is not modified, thus 

 determining whether the modification is transmitted with 

 the micronucleus. By the methods recently devised by Sonne- 

 born and by De Garis, such a test may come soon. 



We may attempt now a summary of the established facts 

 as to the inheritance of acquired environmental characters in 

 unicellular animals. Some of the inherited characteristics 

 manifested by these organisms are consequences of the type 

 of environment under which their ancestors have lived; in 

 some cases ancestors hundreds of generations earlier. A 

 changed environment induces a change in the genie materials 

 that persists long after removal from the conditions that in- 

 duced the change. And this altered genie material, as it 

 assimilates, grows and multiplies, produces, not the original 

 type of material, but the modified type. This continues for 

 many generations. 



Neither the original characteristics nor the modified char- 

 acteristics are fully stable. The original characteristics are 

 found to become modified as the conditions alter. In this 

 respect they are like the modified characters; these too become 

 altered again when the original conditions are restored. 

 There is then a return to the original characteristics, and this 

 return is to be expected on the same ground that the modifi- 



