22 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 slight 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 Griafin 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 alike 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, 7.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- 
