2 2 Experimental Zoology 



one of the factors in the results, can be caused artificially either 

 by a high or by a low temperature. In a mixture of proteids 

 we might expect some sHght differences in the results of coagu- 

 lation, even if the principal changes are the same, and it is not 

 improbable that such minor differences do exist. 



An excellent general review of the effects on the colors has 

 recently been given by Grafin Marie von Linden. She points 

 out that in the Vanessa series, a higher temperature makes the 

 red or yellow deeper or more fiery. The dark background 

 suffers a reduction. Cold gives the reverse, a brightening of 

 the general dark ground color, the yellow expanding at the cost 

 of the red. There is also a lightening of the red and increase 

 of white scales. Extreme heat and cold, as stated above, give 

 remarkably similar results. The black spots on the border run 

 together, so that the peripheral dark spots are lost. The dark 

 border zone becomes clearer (in some forms only at the tip). 

 Despite this peripheral clearing up, extreme temperatures cause 

 an increase of dark pigment elsewhere. It may be said, there- 

 fore, that extremes of heat and of cold do not give specific effects, 

 but produce the same physiological change. 



As a result of these changes the differences between related 

 species sometimes seem to disappear to a greater or less extent. 

 The nearer the forms experimented upon, the more ahke are 

 their aberrations. This result led Fischer to the conclusion 

 that extreme heat and cold cause an atavistic return to the primi- 

 tive type of all the Vanessas, i.e. a return to the stem-form from 

 which they have come. He attempts to explain this result on 

 the grounds that during the development of the color the butter- 

 fly passes in its ontogeny through phylogenetic stages. Cold 

 and heat cause an arrest of development, so that an ancestral 

 stage emerges. 



Standfuss, on the other hand, looks upon the changes as some- 

 thing new, and points out certain contradictions to Fischer's 

 idea that the aberrations are atavistic. For instance, the males 

 are much less prone to atavism than the females, and yet pro- 

 duce a much greater number of aberrations. He thinks it im- 



