730 INHERITANCE 



generations, during which the distinctive features of that stage (imma- 

 turity, maturity, or the like) are transmitted to descendants. 



Second, there are inherited degenerative changes, resulting from life 

 under unfavorable conditions. 



Third, there are adaptive changes, fitting the organism to a changed 

 environment — inherited acclimatization, or immaturity. 



Fourth, there are inherited changes in form and structure, apparently 

 neither adaptive nor degenerative, occurring under the influence of spe- 

 cific environmental conditions. 



Fifth, forming perhaps an additional type, there are inherited varia- 

 tions in form, size, and other characters, that are not obviously due to 

 environmental conditions. 



Some of these five types fall under Jollo's concept of Dauermodif- 

 kationen: changes produced under the influence of environmental condi- 

 tions, inherited for many generations after removal from those conditions, 

 but gradually fading out to final disappearance. This includes the third 

 and fourth types above, and, according to Jollos's view, also the fifth. 

 The first type obviously appears not to fall under this concept, and the 

 second type is not known to disappear upon restoration to a more favor- 

 able environment. 



Most of thesb types of modification may disappear or be altered upon 

 the occurrence of sexual reproduction. In type 1, the condition of matur- 

 ity changes at sexual reproduction into one of immaturity. In type 2, the 

 inherited degenerative changes in many cases disappear at sexual repro- 

 duction ("rejuvenescence through conjugation"), but it is a notable fact 

 that in some cases they do not. In type 3, the inherited acclimatization and 

 immunity likewise often disappear at sexual reproduction, though again 

 in some cases they do not. In types 4 and 5, the efi^ect of sexual repro- 

 duction is not known. 



These inherited modifications, so far as they can be brought under 

 the concept of Dauermod'ifikationen, are held by Jollos to have their 

 seat in the cytoplasm only, the genetic materials of the chromosomes being 

 unchanged. This is based in the main on the fact that the inherited 

 modifications grow less and finally disappear, when the organisms are 

 restored to environments that do not produce the modifications. A change 

 in the genetic materials of the chromosomes ("mutation"), it is held, 

 would be permanent; it would not disappear after many generations in 



