38 THE CANADIAN ENTOMOLOGIST. 
body the forewings are slightly discoloured with dusky scales. On the 
Fig. 7. under surface the wings are sometimes of 
MA 2 yellowish hue, with the veins broadly 
=} marked with black ¢ or dark green; some: 
veins merely faintly dutinets in black ; 
between ‘these two extremes many aie 
tions of shade may be observed. The 
pure white specimens found in the North 
West were supposed at one time to be a 
——————— — distinct species, and were described by 
ane ie i name of the “Chaste Butterfly” (P. Casta) ; there is no 
doubt now, however, that these are merely varieties of the same species. 
The legs and body of the insect are black ; its wings expand to a breadth 
of about two inches, but there is considerable variation in the size. of 
individuals. 
The butterfly, about the end of May or beginning of June, and again 
towards the close of summer, may be seen hovering over the food-plants 
of its larvæ, preparing to deposit its eggs. These are pear-shaped, or 
oval, of a yellow-green colour, and measure about one-twentieth of an 
inch in length, and a third of this amount in diameter ; they are ribbed 
longitudinally with about fifteen sharp-edged lines. The parent deposits 
them singly, andrarely more than one on a leaf, on the underside of the 
lcaves gt the cabbage, turnip, radish, mustard and other plants of the 
order Crucifere. ‘They are hatched in about a week or ten days. 
The young larva is pale green, cylindrical in shape, and covered with 
short, whitish hairs. In order to escape from the egg it makes an opening 
with its jaws and then eats the shell until the aperture is large enough to 
admit of its easy egress ; it subsequently devours the greater part of the 
shell that remains. ‘At first the new-born caterpillar is less than one- 
twelfth of an inch in length, but it grows rapidly, until it attains its full 
size, about an inch and a quarter, in the brief space of a fortnight. The 
mature larva (Fig. 7, a) is pale green in colour, with numerous darker dots 
and a dark line along the back ; it closely resembles the ribs of the leaf 
upon which it feeds. 
When mature, the caterpillar forsakes its food plant and crawls away 
to some secluded spot, such as the under side of a stone or board, or a 
crevice in a fence or wall; there it spins a knot of silk to which it fastens 
its hindermost pair of feet ; then it proceeds to form a loop of silk which 
