254 f^P"""' 
3rd. If not, i. e., if some of those pupse lie over through autumn and winter, are 
the insects produced in the following spring illustraria or delunaria ? I ask 
particular attention to question two. In Vol. I., p. 44 of the " Ent. Weekly Intel- 
ligencer" I find the foUo-wing communication from Mr. Machin : — " I took two of 
" the larva of this insect on the 22nd of July of last year, about half- fed ; two 
" larger ones were taken the same day by Mr. J. Standish, and bred by him in the 
" following month ; these Mr. Standish called suhlunaria, and considered them quite 
" distinct from illusl/raria. My two larvae kept feeding, though very slowly, till the 
" end of September, when they changed to pupse. Being fully convinced in my 
"own mind that the two bred by Mr. Standish were from an early brood of illus- 
" traria, I determined in the autum to try and procure a number of the larvae. I 
" succeeded in obtaining about 25, several on the 12th of September, but a few 
" days old, &c." Now, were these four larvae the result of spring-laid eggs ? 
There is an ambiguity in Mr. M.'s statement, which leaves this uncertain. From 
his saying that he was fally convinced that Mr, Standish' s two larvae were from an 
early brood, we are left to infer that he considered his own were not, i. c, that the 
larger ones were the progeny of the spring brood, while his (the smaller) were 
born of summer parents. Yet at the close of his communication he speaks of 
having procured 25 larvae, several on the 12th of September, only a few days old. 
Surely the two found July 22nd, and half-fed, and these latter can not both have 
been summer born ? This by the way. If (as I assume) Mr. Machin's two larvae, 
which fed on slowly throughout September, and passed the winter state, were 
spring bom, what came out the following spring — illustraria or dehmaria ? If 
delunaria, then Dr. K.'s thermal theory fails ; for, owing to retardation, they 
ought to have produced illustraria, if I understand him rightly. On the other 
hand, if they did produce illustraria, then I would venture to suggest that this 
result was much more probably caused by prolongation of the larval than the 
PUPAL state. Let me apply this suggestion to illustraria generally. I must be 
permitted to assume (most willingly subject to correction, if wrong) that the 
spring larvas feed up in a shorter time than the autumnal. If this be true, is it not 
highly probable that the smaller and paler progeny of the former, and the larger 
and darker progeny of the latter are respectively due, rather to the shorter and 
longer duration of the larval than the pupal state ? I should unhesitatingly adopt 
this conclusion, if I were only certain of my premises. One circumstance appears 
to me to give great force to my explanation, and it is this : illustraria is much 
larger than dehma/ria. Now, whatever may be said as to colour, it is obviously 
impossible that increased size can be obtained in the pupal state. It must be due 
to some previous stage of the insect's existence ; and what can this be but the 
larval ? But again, with regard even to colour. In a communication made by 
Mr. Hopley on this siibject (B. M. M., p. 212), he says, in reference to Ardia Caja, 
that he thinks he has reason to believe that light, more or less, in the larval 
state, has an influence upon the colouring of the future imago ; that much light 
will produce darker specimens, and little light paler. Mr. Hopley being, I 
believe, an artist, we may presume that he is correct in thus describing the effect 
of a greater or less degree of light. Applying this canon to the case before us, the 
winter pupae of illustraria, being so much longer shrouded in darkness, ought, in 
