No. 583] BOLE OF ENVIRONMENT IN DROSOPHILA 427 



to multiple factors or to environmental effects. That 

 the former rather than the latter is the main explanation 

 is shown in the frequency with which the abnormal flies 

 appear in the inbred stock (where the conditions are the 

 same as in the experiments) and the rarity with which 

 the character appears when the stock is outcrossed. 



THE NON-INHERITANCE OF AN ACQUIRED CHARACTER 



The acquirement of a new character by a pure stock 

 implies by definition the capacity of this stock to respond 

 to the imposed conditions. Conversely if an animal does 

 not acquire a new character in a changed environment it 

 does not come within the scope of the definition of an 

 acquired character, and even should its offspring show 

 new characters as a result of the new environment in 

 which the parents have been placed the result is still 

 excluded by definition from being a case of the inheri- 

 tance of an acquired character. At least this is my un- 

 derstanding of the use of the term and the way in which 

 I shall use it in the following statement. 



The mutant stock of abnormal abdomen offers an ex- 

 ceptional opportunity to examine the possible influence 

 of an acquired character on the offspring. As the experi- 

 ments have shown this stock is very susceptible to en- 

 vironmental influence, and the effects produced pro- 

 foundly affect the structure of the organism. Moreover 

 it is possible to carry the stock through several genera- 

 tions in either of the phenotypic conditions, and then, at 

 will, to cause the other type to appear at once in its com- 

 pletest form, by regulating the external conditions in 

 which the young are reared. 



No better material could be found for studying the 

 possible influence of the environment through its effects 

 on the soma of the individual. The evidence shows in the 

 clearest manner that the condition of the parent, whether 

 normal or abnormal in type, has no effect on the charac- 

 ter of the offspring. The evidence is so clear and so 

 positive that it seems unnecessary to elaborate the point. 



