phase, and I believe there is not in either of the species even a 
tendency to alternate generation. 
STAGES IN WHICH TEMPERATURE OPERATES. 
The next question that arises is : What is the right stage at which 
the determining temperature should be applied? It must of course 
be before the time whén the imago is formed and perfected. I 
have tested this in S. bi/unaria, — using temperatures which are 
adequate to operate effectively in the stages of egg onwards, — 
as far back in the ontogeny as the lifetime of the parents, 
before the union between them, and therefore from an early 
stage of the germ plasm. 
EGG STAGE. 
As to the first of these stages, that of the egg, I have seen no 
reason to believe that the phase to be assumed depends on what 
takes place in that stage (or in the earlier ontogeny). In 1894, at 
the suggestion of my friend DR. DIXEY (now the President of 
the Entomological Society of London), I tried a long series of 
experiments with eggs of Selenia tetralunaria, exposing them for 
from seven to forty days, to various temperatures ranging from 
80° E. (27° C:) to 33° F. (1° C.), but this differential treatment, 
though, as might have been expected, greatly accelerating or 
retarding the hatching of the egg, made no difference whatever 
in the habit or aspect of the perfect Insect. Since then I have 
tried similar experiments with S. bilunaria, and with similar want 
of effect. The stages, in which this external influence can operate, 
may therefore be considered to be those of the larva and pupa; 
the former being the stage of growth, never I think less than 
many hundredfold, sometimes many thousandfold, comprising 
also considerable changes in structure and sometimes in habits; 
the latter a stage of external fixity and quiescence, with vast 
internal changes of structure, but loss instead of gain in mass. 
PUPAL STAGE. 
The very conspicuous results on the facies of Lepidoptera produc- 
ed by exposing the pupa to abnormal temperatures have directed 
