38 



THE CANADIAN ENTOMOLOGIST. 



body the forewings are slightly discoloured with dusky scales. On the 

 *£• 7 * under surface the wings are sometimes of 



.a yellowish hue, with the veins broadly 

 [marked with black or dark green; some- 

 times they are entirely white, with the 

 veins merely faintly outlined in black ; 

 between these two extremes many grada- 

 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 

 Kirby under the 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 larvas, 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, and rarely more than one on a leaf, on the underside of the 

 leaves 01 the cabbage, turnip, radish, mustard and other plants of the 

 order Crucife?'cz. 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 



