2i 4 TRANSMISSION OF ACQUIRED CHARACTERS 



A Typical Case. An often-quoted and typical instance was 

 communicated to Darwin by Moritz Wagner. Some pupae of 

 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 pupae of 

 Vanessa urti&z 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 



