214 TRANSMISSION OF ACQUIRED CHARACTERS 



a Texan species of Saturnia were brought in 1870 to Switzerland. 

 In May, 1871, the moths emerged and were entirely true to type ; 

 they had young, and these were fed on the leaves of Juglans regia 

 (the Texan form feeding on Juglans nigra) ; these young developed 

 into moths so different in colour and form from their parents 

 that some entomologists referred them to distinct species. This 

 was a well-marked individual modification, but the story stops 

 just where it was beginning to be interesting. We are not told 

 about the subsequent generations. If they, too, were fed 

 on Juglans regia, and reared in Switzerland, they probably 

 reproduced the new type, but this would simply mean that 

 the modification was re-impressed on successive generations. 



Experiments on Lepidoptera. Standfuss reared pupa of 

 Vanessa urticcz 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. 



