Effect of temperature on development 259 
The reader will notice that the aberrations produced at a very 
low temperature (from 0° to — 20°C.) are absolutely identical with 
the aberrations produced by exposing the pupae to extremely high 
temperatures (42° to 46°C.). Moreover the aberrations produced by 
a moderately low temperature (from 0° to 10°C.) are identical with 
the aberrations produced by a moderately high temperature (36° to 
41° 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 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 (@) (e.g. hydro- 
lyses) causes or furnishes the material for a second reaction or group 
of reactions (0) (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°. 
But we know also that the temperature coeflicients do not vary 
equally for 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 (6). If 
therefore a certain substance is formed at the normal temperature 
of the animal in such quantities as are needed for the catenary 
reaction (6), it is not to be expected that this same perfect balance 
will be maintained for extremely high or extremely low tempera- 
tures ; 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. Tue Errects or 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 
17—2 
