104 THE CANADIAN ENTOMOLOGIST. 
especially near the body. ‘The illustrations on page 83 of the Report of 
our Society for 1871, published by the Ontario Department of Agriculture, 
give an exact idea of the insect at this season. ‘This change in colour 
has been noticed in England ; indeed, before its progressiveness had been 
observed, an eminent entomologist there separated the spring and autumn 
broods into distinct species. I quote from a letter received in 1864 from 
- my friend Dr. Jordan, of Birmingham :— 
“You are probably aware that here in Dana we have two distinct 
broods of the insect, the first appearing in April, the second in July. The 
first almost wants the apical spot on the top wing in both sexes, and on 
the male the central spot is often also quite obliterated. To this the 
name of P. metra was given by Stephens, who then supposed it a distinct 
species. In the autumnal brood, or typical P. rapæ, we have a larger 
and darker insect, with the spots more marked, and the black patch at 
the apex of the fore wing very much darker.” 
The yellow variety also shares in this progressive change of colour. 
The spring specimens are of a very delicate yellow, almost without spots, 
and are very handsome, while those appearing in the fall are of a sulphur 
yellow, and heavily marked. 
Dr. Jordan speaks of there being two broods of the insect in England. 
I think that in Canada they are more numerous. It is impossible, how- 
ever, to settle the number with certainty, as one brood encroaches on the 
next ; and from the time when the butterflies begin to deposit their eges 
on cabbage plants in the hot-beds, in April and May, until October, larve 
of all sizes and ages may be found feeding on the same plant. The short 
time required for the complete developement of the insect also favours the 
idea of there being three or more broods in one season. Some caterpillars 
reared by me in June, 1864, grew from one-twelfth of an inch in length to 
their full size, in eleven days; they then became pupæ, and seven days 
afterwards, the perfect insects were produced. Allowing for the influence 
of temperature in accelerating or retarding their changes, thirty days 
would be a fair average to give as the duration of each brood, and this 
would be equal to four or five broods in the season in the latitude of 
Quebec. In fact, there is no other way of accounting for their surprising 
numbers in the latter part of summer. 
, I have not yet met with any parasite infesting this butterfly, though I 
have found pupæ which had apparently been destroyed by them; and a 
fellow-student here (Mr. Caulfield) informs me that he now has about 
twenty chrysalids containihg some insect enemy. The most powerful 
