aberration found at the high as well
as at the low temperature limits. This cause he seems to find in the
inhibiting effects of extreme temperatures upon development.

If we try to analyse such results as Fischer's from a physico-chemical
point of view, we must realise that what we call life consists of a
series of chemical reactions, which are connected in a catenary way;
inasmuch as one reaction or group of reactions (a) (e.g. hydrolyses)
causes or furnishes the material for a second reaction or group
of reactions (b) (e.g. oxydations). We know that the temperature
coefficient for physiological processes varies slightly at various parts
of the scale; as a rule it is higher near 0 and lower near 30 deg. But
we know also that the temperature coefficients do not vary equally from
the various physiological processes. It is, therefore, to be expected
that the temperature coefficients for the group of reactions of the type
(a) will not be identical through the whole scale with the temperature
coefficients for the reactions of the type (b). If therefore a certain
substance is formed at the normal temperature of the animal in such
quantities as are needed for the catenary reaction (b), it is not to be
expected that this same perfect balance will be maintained for extremely
high or extremely low temperatures; it is more probable that one group
of reactions will exceed the other and thus produce aberrant chemical
effects, which may underlie the colour aberrations observed by Fischer
and other experimenters.

It is important to notice that Fischer was also able to produce
aberrations through the application of narcotics. Wolfgang Ostwald has
produced experimentally, through variation of temperature, dimorphism of
form in Daphnia. Lack of space precludes an account of these important
experiments, as of so many others.

IV. THE EFFECTS OF LIGHT.

At the present day nobody seriously questions the statement that the
action of light upon organisms is primarily one of a chemical character.
While this chemical action is of the utmost importance for organisms,
the nutrition of which depends upon the action of chlorophyll, it
becomes of less importance for organisms devoid of chlorophyll.
Nevertheless, we find animals in which the formation of organs by
regeneration is not possible unless they are exposed to light. An
observation made by the writer on the regeneration of polyps in a
hydroid, Eudendrium racemosum, at Woods Hole, may b