e million times. Since this prolongation of life is far
in excess of the retardation of development through a lowering of
temperature, it is obvious that, in spite of the retardation of
development in Arctic seas, animal life must be denser there than in
temperate or tropical seas. The excessive increase of the duration of
life at the poles will necessitate the simultaneous existence of more
successive generations of the same species in these regions than in the
temperate or tropical regions.

The writer is inclined to believe that these results have some bearing
upon a problem which plays an important role in theories of evolution,
namely, the cause of natural death. It has been stated that the
processes of differentiation and development lead also to the natural
death of the individual. If we express this in chemical terms it means
that the chemical processes which underlie development also determine
natural death. Physical chemistry has taught us to identify two chemical
processes even if only certain of their features are known. One of
these means of identification is the temperature coefficient. When two
chemical processes are identical, their velocity must be reduced by
the same amount if the temperature is lowered to the same extent.
The temperature coefficient for the duration of life of cold-blooded
organisms seems, however, to differ enormously from the temperature
coefficient for their rate of development. For a difference in
temperature of 10 deg C. the duration of life is altered five hundred
times as much as the rate of development; and, for a change of 20 deg
C., it is altered more than a hundred thousand times as much. From this
we may conclude that, at least for the sea-urchin eggs and embryo,
the chemical processes which determine natural death are certainly not
identical with the processes which underlie their development. T.B.
Robertson has also arrived at the conclusion, for quite different
reasons, that the process of senile decay is essentially different from
that of growth and development.

(b) CHANGES IN THE COLOUR OF BUTTERFLIES PRODUCED THROUGH THE INFLUENCE
OF TEMPERATURE.

The experiments of Dorfmeister, Weismann, Merrifield, Standfuss,
and Fischer, on seasonal dimorphism and the aberration of colour in
butterflies have so often been discussed in biological literature that
a short reference to them will suffice. By seasonal dimorphism is meant
the fact that species may appear at different