204 Life and Death, Heredity and Evolution 



and a desire for further tests before judgment is passed as to 

 the inherited effects of environmental action on the germ 

 cells, in higher organisms ; more work along these lines is 

 greatly needed. 



But the results set forth are, in all cases save perhaps 

 certain of those described by Kammerer, of the sort that 

 agree in principle with the inherited effects of environmental 

 action in the lower organisms, as described in Lecture 4. 

 The action of the external agents was directly on the germ 

 cells, modifying the primary (directly transmitted) heredi- 

 tary characters. In consequence the later or secondary 

 characters were altered. Such cases are perhaps better 

 established in the Protozoa and bacteria than in higher 

 organisms. 



As to the nature and extent of the changes in hereditary 

 characters arising in higher organisms, aside from the direct 

 effects of environmental action, an enormous volume of work 

 has been done. In higher organisms it is a prevalent con- 

 viction that changes in the hereditary characters occur by 

 mutation. What relation has this and the facts on which 

 it is based to the hereditary changes seen in the Protozoa, 

 in such a case as Difflugia, for example? 



The concept of mutation has been based, in different 

 minds, on a number of different points, sometimes held 

 separately, sometimes together. One basis for the distinc- 

 tion of mutations from other variations is this: Many 

 variations in the characteristics of organisms are not in- 

 herited; such are the common superficial effects of environ- 

 mental diversities. We have given illustrations of this in 

 our account of the Protozoa. It is therefore convenient to 

 have a distinctive name for those that are inherited, and 

 some call these mutations. In this usage, of course it is a 

 mere matter of definition to state that any new heritable 



