seasons of the year in a
somewhat different form or colour. Vanessa prorsa is the summer form,
Vanessa levana the winter form of the same species. By keeping the pupae
of Vanessa prorsa several weeks at a temperature of from 0 deg to 1 deg
Weismann succeeded in obtaining from the summer chrysalids specimens
which resembled the winter variety, Vanessa levana.

If we wish to get a clear understanding of the causes of variation in
the colour and pattern of butterflies, we must direct our attention to
the experiments of Fischer, who worked with more extreme temperatures
than his predecessors, and found that almost identical aberrations
of colour could be produced by both extremely high and extremely low
temperatures. This can be clearly seen from the following tabulated
results of his observations. At the head of each column the reader
finds the temperature to which Fischer submitted the pupae, and in the
vertical column below are found the varieties that were produced. In the
vertical column A are given the normal forms:

(Temperatures in deg C.)

0 to -20 0 to +10 A. +35 to +37 +36 to +41 +42 to +46
(Normal forms)

ichnusoides polaris urticae ichnusa polaris ichnusoides
(nigrita) (nigrita)

antigone fischeri io - fischeri antigone
(iokaste) (iokaste)

testudo dixeyi polychloros erythromelas dixeyi testudo

hygiaea artemis antiopa epione artemis hygiaea

elymi wiskotti cardui - wiskotti elymi

klymene merrifieldi atalanta - merrifieldi klymene

weismanni porima prorsa - porima weismanni

The reader will notice that the aberrations produced at a very low
temperature (from 0 to -20 deg C.) are absolutely identical with
the aberrations produced by exposing the pupae to extremely high
temperatures (42 to 46 deg C.). Moreover the aberrations produced by a
moderately low temperature (from 0 to 10 deg C.) are identical with the
aberrations produced by a moderately high temperature (36 to 41 deg C.)

From these observations Fischer concludes that it is erroneous to speak
of a specific effect of high and of low temperatures, but that there
must be a common cause for the