SUPPOSED TRANSMISSION OF ACQLflRED CHARACTERS 465 



temperature in the germ-plasm to a much slighter extent than 

 in the rudiments of the wings. If the modifying influence had the 

 same effect in both cases, the germ-plasm in the germ-cells of 

 a butterfly of the summer generation would be modified as much 

 as the wings of the same individual ; and consequently the off- 

 spring, even if exposed to a low temperature, would necessarily 

 display a greater tendency towards the summer coloration, 

 because the latter was already potentially contained in the germ. 

 This, then, would only be the case if the influence of the cold 

 were stronger than that of the heat. In any case, however, a 

 coloration intermediate between that produced by cold and by 

 heat respectively would result, and would be transmitted to both 

 generations, even when the two influences were equally strong. 

 If we indicate the winter and summer colorations respectively 

 by A and B, the coloration of each generation would then be 

 I A 4- I B. It is only when the germ-plasm is modified to a much 

 smaller extent than the determinants which have already entered 

 the rudiments of the wings, that an alteration of coloration can 

 become permanent. 



In many other animals and plants influences of temperature 

 and environment may very possibly produce permanent heredi- 

 tary variations in a similar manner; but it is diflicult — in fact 

 almost impossible — to identify such cases with anything like 

 certainty from the observations which have hitherto been made. 

 Thus we find it stated that ' in Cashmere dogs soon become 

 covered with a woolly hair ; ' * but we do not know who observed 

 this, or who ascertained that such a change — if it really does 

 occur — is transmitted. 'Merino sheep lose their fine wool when 

 they are transported to a tropical climate ; ' but I have not been 

 able to discover whether this loss occurs in the first, or in the 

 course of several, generations. We are thus left in uncertainty 

 as to the possibility of a direct climatic variation of a somatic 

 part having taken place in these instances, which would again 

 disappear in the next generation provided that the descendants 

 were placed under the original climatic conditions. The same 

 applies to the races of naked dogs from the tropics, such as the 



* These statements are quoted from an essay by Giard, who takes 

 them as a proof of the transmission of somatogenic modifications. Cf. 

 ' L'Heredite des modifications somatiques,' Revue Scientifique, December 

 6th, 1890. 



