214 TRANSMISSION OF ACQUIRED CHARACTERS 



directly on the eggs. This seems the more likely since the 

 differences between the two types (in shape of tail, details of 

 bristles, etc.) are not such as we can interpret as the natural 

 direct results of altered salinity. It is well known that slight 

 alterations in the physico-chemical composition of the water 

 have sometimes a great and mysterious influence on eggs and 

 developing embryos. Furthermore, the species of Artemia 

 seem to be very variable, and there is a series of intermediate 

 forms connecting Artemia salina and Artemia milhausenii. 

 Perhaps the altered salinity simply pulled the trigger of varia- 

 bility. 



But if the changes were somatic modifications, it is still open 

 to the critic to point out that Schmankewitsch experimented 

 with a progressively changing environment on a series of genera- 

 tions, and that the results were due to modifications hammered 

 afresh on each successive generation, without there being any 

 inheritance of these modifications. 



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. 

 The same seems to be true in regard to most of the climatic 

 changes of which we have authentic information. 



Experiments on Butterflies. — Some very interesting experi- 



