EFFECTS OF CHANGED ENVIRONMENT 215 



ments have been made, especially by Standfuss and Fischer, 

 who subjected pupae of butterflies to abnormal temperatures, 

 observed the subsequent modifications on the fully formed 

 insects, and showed that these were repeated in their progeny. 



Standfuss reared the pupae of the common Vanessa urticce 

 at a lower than the normal temperature, and obtained a northern 

 type (var. polaris) ; he reared them at a temperature higher than 

 the normal, and obtained a southern variety (var. ichnusa). 

 In the progeny he found a very small percentage (all males) 

 which showed a change in the same direction as the parents. 



Fischer worked with Arctia caja, reared the pupae at 8° C, 

 and obtained some unusually dark forms. Two of these were 

 paired and their progeny was reared at the normal temperature. 

 A small percentage of these — the last of the brood to emerge 

 from the pupa-state — showed the same kind of melanistic pecu- 

 liarity as the parents had shown. 



Fischer pointed out, however, that the colour-aberration in 

 the offspring was not a repetition of the parental peculiarity, 

 though it was in the same direction and sometimes went farther. 

 He did not regard the case as illustrating the transmission of a 

 specific modification, but agreed with Weismann's interpretation 

 that the germ-cells had been prompted to vary by the lowered 

 temperature. It should also be noted that in many butterflies 

 there is a strong constitutional — i.e. germinal — tendency to 

 melanistic variation, that the aberration does not occur in all the 

 individuals subjected to the low temperature, that it occurs in 

 very diverse degrees, and that the experimenter selected two 

 forms to pair together. 



Americanisation of Irishmen. — Herbert Spencer thought that 

 the best examples of inherited modifications occur in mankind. 

 " Thus in the United States the descendants of the immigrant 

 Irish lose their Celtic aspect, and become Americanised. . . . 

 To say that ' spontaneous variation,' increased by natural 

 selection, can have produced this effect is going too far." If 



