1867.] 255 
spring, to produce paler gpecimena, but thoy are much darker. If, now, we admit 
the longer larval duration of the summer born progeny, we have a proportionate 
prolongation of light, and the result is, darker specimens of the perfect insect 
next spring. But Dr. K. says, '• Whenever the completion of the pupal stage is 
" accelerated, then delunaria, produces dehmaria," — that is, as I take it, if the pupae 
(which are the result of summer-laid eggs, and which, under ordinary circumstances, 
would pass the winter in that state, and then produce illusi/raria) are, by some 
artificial or unusual means, forced— then the result would be dehmaria. Is this 
indeed the case ? Has it ever been proved ? If so, it appears to me a most extraor- 
dinary circumstance ; and of coui-se I admit that, so far as it goes, it militates 
against my theory, and, to the same extent, justifies Dr. Knaggs, as he himself 
remarks, in inferring the converse. As I am so much i n the dark about the habits 
of illustraria, I will not say more about it at present, but shall feel truly obliged 
to any one who will give a full, minute, and accm-ate account of the history of this 
insect, especially whether there be any well authenticated case or cases of delunama 
eggs producing delunaria insects through the pupae having been forced. However, 
admitting this, it is but one instance opposed to many, for I think Dr. Knaggs 
scarcely allows sufficient weight to those I have already adduced against the 
thermic theory. I have brought forward nine species in my favour — he only one, 
viz., illustraria; and upon this one he rests satisfied. " I therefore feel justified 
'' in coming to the conclusion that acceleration or retardation of the completion of 
" the pupal state are causes of a greater or less degree of variation in the imago." 
Let me now put forward a few additional facts. In the cases already adduced 
(and many others might be given), retardation only was alluded to ; nature was 
left to herself, and no variation was perceptible. How is it when artificial means 
are employed to accelerate the pupal state ? For many years I have been in the 
habit of " forcing " pupae. The method is immaterial. Suffice it to say, that I have 
bred the following insects at the following periods : — During the last three weeks 
of March, Ewpithecia centaureata and coronata, Coremia ferrugata, Macaria litv/rata, 
Fidonia piniaria, Clostera curtida and reclusa ; Notodonta dromedarius, trepida, 
dodoncea, chaonia, cuculUna, dictwa, camelina; Acronycta 'rnegacepliala and meny- 
anthidis. Now all these were at least two months earlier than they would appear 
in a state of nature ; yet in no case was there any appreciable variation either in 
colour or form. I may add that, at the time these insects were bred, my attention 
was particularly drawn to this part of the question, from the fact that it had been 
supposed "forcing" was calculated to produce cripples, or pale specimens. It 
was certainly not so in my case, as may be seen by referring to my communication 
(Intelligencer, Vol. I., p. 11). Curiously enough at this date (March 2nd) when I 
am wiiting, I have on my setting-boards specimens — forced, of course — of Eupi- 
thecia virgaureata, albipunctata, venosata ; Saturnia carpini, and Platypteryx ungui- 
cula, all of which emerged in February ; yet not the slightest variation in any is 
discernible. I have also had Smerinthus tiliw and ocellatus out in February, in 
fact, scores of species in that month and March ; yet in not one single instance 
can I remember to have seen any aberi'ation in form or colom'iug. In fact, I have 
been exceedingly unfortunate in breeding varieties. 
Now I am sure Dr. Knaggs will pardon me for thinking that these and the 
