140 HEREDITY AND SELECTION IN SOCIOLOGY 



undoubtedly exerts a strong influence on tlie pupa. At a tem- 

 perature of + 10° C, he was able to produce tbe northern variety 

 from the pupa developed from the egg of an individual of the 

 southern variety ; and at a temperature of + 38° C, the contrary 

 result was obtained, the southern variety being produced from 

 the pupa of a northern egg. The subsequent experiments of 

 Standfuss and Merrifield have shown that, by lowering the 

 temperature to —8° C, it is possible to obtain aberrations 

 from the normal type in the case of species of Vanessa ; and these 

 aberrations represented more or less a return to an ancestral 

 type, as was proved by a comparative study of the colouring 

 of the wings in the different Vanessa species. It may be said 

 that this sudden transformation of the Vanessa under the in- 

 fluence of low temperature is similar to the mutations observed 

 by De Vries in plants under cultivation. But a distinction may 

 be drawn between the two cases ; in the one case a sLugle brusque 

 change of temperature suffices to modify the colouring of the 

 wings, whereas in the other case the mutation is preceded by a 

 more or less prolonged period of premutation, during which the 

 readaptation of the reproductive parts is proceeding, becoming 

 at length suddenly manifest in the mutation. There is, never- 

 theless, an analogy in so far as mutations are also the result 

 of the action of environing conditions. 



The aberrations brought about by the lowered temperature are 

 expHcable on the supposition that the determinants of the wings 

 are, in the pupa stage, subjected to different degrees of influence, 

 with the result that some determinant species are strengthened, 

 others weakened ; so that the colouring on the developed wings 

 is unequally developed as compared with the normal type, the 

 sphere of colouring being in one part above the normal, in 

 another part below the normal, in a third part entirely suppressed. 

 By this alteration of the balance of the colour determinants a 

 return to an ancestral type is obtained ; thus, we must conclude 

 that in the germ-plasm of the modern Vanessa species a number 



