50 THE BOOK OF BRITISH BUTTERFLIES. 



The eggs, which are laid first in April and May, and 

 again in July and August, may be found on Cabbages and 

 other cruciferous plants, as well as on Mignonette, Nastur- 

 tiums, &c. The larvae of the first brood hatch in just 

 under a fortnight, those of the second in about ten days. 



In about three weeks the caterpillars (Fig. 29) are full- 

 grown, being then about ijin. in length, and green in 

 colour, somewhat darker on the dorsal than on the ventral 

 surface, the two tints being separated by a line of yellow 

 spots in pairs along the spiracular region. There is also 

 a yellow stripe along the middle of the back. The 

 divisions between the segments are not clear, and each 

 segment is divided into half-a-dozen transverse sections. 

 The head and body are covered with numerous tiny warts, 

 mostly black, each of which bears a very short, slender 

 hair. 



The chrysalis (Fig. 31), which is light grey usually, 

 though sometimes tinged with red or green, is marked 

 with black dots, which are, however, neither so large 

 nor so numerous as in the case of P. brassicce. A few 

 dots larger than the rest are found chiefly on the points 

 of the projections, which are just tipped with pale yellow. 

 There is a medio-dorsal keel as well as a pair of lateral 

 ones, the first having a high prominence on the thorax, 

 and the latter one near the tip of each wing-case. This 

 chrysalis, though slender, has a rather rigid appearance. 

 Very dark specimens are occasionally found. 



The imago (Fig. 27), which appears first in April, and is 

 on the wing all the summer through, with the exception of 

 a short period about the end of July, has all the wings 

 rounded, the costal margin arched, and the tip obtusely 

 pointed. The upper surface has at the tip of the fore- 

 wings a dusky mark much less decided than in P. brassicce, 

 a small black spot (absent in the male of P. brassicce) in 



