442 THE ZOOLOGIST. 



pupal stage. Albinic varieties were produced by subjecting the 

 pupae to a more considerable increase or decrease of temperature. 

 Such changes were not inherited. But if the altered tempera- 

 ture was maintained during the adult stage some of the offspring 

 were found to be similar to their parents. This effect was traced 

 to the action of the environment on the germ-cells themselves 

 during their maturation. For, if normal beetles were placed in 

 changed conditions during the maturation of some of their eggs, 

 and put back into normal conditions during the maturation of 

 others, the adults arising from the first batch of eggs showed 

 aberrations, whilst those from the second did not. The aberra- 

 tions produced by the action of the changed environment on the 

 maturing germ-cells were inherited completely — that is to say, 

 individuals exhibiting such variations bred true in normal con- 

 ditions, and when crossed with the parent form a typical 

 Mendelian segregation occurred in the second generation, in 

 each case the original form acting as a dominant to the variety. 

 Now, if these beetles had been kept constantly in a changed 

 environment, it would have appeared that the aberrations in- 

 duced in the first generation by the environment had been 

 inherited in the next generation ; whereas, in reality, in the first 

 generation the variation is merely a fluctuation, in the second it 

 is of the nature of a mutation. When once the germ-plasm has 

 been changed, it is natural that every individual resulting from 

 that germ-plasm should show the same change, and this is 

 exactly what Tower found. 



We cannot, therefore, claim that these experiments support 

 the inheritance of acquired characters, as at first sight they 

 appear to do. On the contrary, acquired characters (i. e. 

 characters produced in the somatic cells) are never inherited. 

 For the changes to be inherited, it is necessary to directly 

 influence the germ-cells. 



The experiments of Standfuss on Vanessa urticce, which were 

 confirmed by Weissman, and those of Fischer on Arctia caja, 

 yielded results which must be briefly considered. Fischer, for 

 instance, found that by exposing the pupae to a temperature of 

 8° C. a certain number of dark aberrant moths resulted. When 

 a pair of these were mated and their eggs reared under normal 

 conditions a certain number of the offspring were dark, but not 



