124 Mr. F. Merrifield’s Report of Progress in 
colour, depth of hue, and, it is alleged, form, that until 
one was bred from the other the two were considered 
distinct species. 
In describing my experience with the several groups 
successively experimented on I begin with those brought 
up under conditions most nearly resembling natural ones, 
as they will afford a convenient standard of comparison 
with such as were reared under more artificial cireum- 
stances. I therefore commence with those illunaria 
which were “‘ sleeved” on growing trees. I am inclined 
to think that—except in the favourable circumstance 
that they were more effectually protected from enemies— 
the sleeved larve differed so little in their surroundings 
from wild-bred ones that they may be taken as fairly 
representative of the latter. I should, however, mention 
that there was one period of their lives during which 
nearly all the sleeved insects were subjected to a higher 
temperature than the natural one. In order to bring the 
moths out as closely together in point of time as possible, 
when the first moth appeared, the remaining pup were 
at once put into the forcing-box. I am not sure that this 
was necessary, especially with the summer brood of 
moths, for my experiments lead me to think that healthy 
individuals of this species, if kept in the dark, will live 
for ten days and more in summer, and for two or three 
weeks or more in colder weather, without any impairment 
of their functions, and only in rare instances will flutter 
so as to damage the tips of their wings enough to prevent 
convenient measurement. 
Some preliminary explanations are necessary as to 
general treatment, and as to the sense in which I have 
used various expressions. My reason for being a little 
particular in these explanations is that any value such 
experiments as I am describing may possess depends 
entirely on a knowledge of the conditions under which 
they were tried. I have not knowingly burdened the 
narration with any statements, except such as seem to 
have some bearing or possible bearing on the results 
obtained. By “eggs,” unless otherwise specified, I mean 
fertile eggs; and by the expression “‘fertile,” as applied 
to the Selenias, I mean such as turn red, though many 
that go through the red stage and even the black one, 
which indicates that the young dark-skinned larva has 
been fully formed, often fail to hatch. As to the expressions 
