84 THE REPORT OF THE No. 33 



lower surface of the leaves close to the leaf veins. Each female is capable of 

 laying a considerable number of eggs, as many as 499 having been deposited 

 on cabbage by a single female under observation. 



The egg is pale greenish yellow to orange yellow in colour, elongate and 

 somewhat bullet-shaped, tapering to a flattened point. It measures approxi- 

 mately 1 mm. from the base to the apex and a little less than 0.5 mm. at its 

 greatest diameter. The surface is raised into ten longitudinal ridges accentuated 

 by numerous small transverse markings. 



The process of hatching occupies about twenty minutes. The larva tears 

 a hole in the shell of the egg, about one-third of the distance from the apex, 

 large enough to admit the passage of its body. On hatching it is pale-yellowish 

 orange in colour and measures 1.5 mm. in length. Shortly after hatching the 

 larva usually completely devours the egg-shell, often eating out a shallow 

 circular depression in the leaf tissues where the egg had rested. Within forty- 

 eight hours after hatching it commences to feed on the leaf tissues, the intestinal 

 tract showing green through the integument due to the ingestion of chloroplasts. 



Feeding takes place fairly slowly up to the third moult, after which the 

 larvae eats voraciously until just before pupating. For some hours previous to 

 moulting the larvae cease to feed and spin a fine platform of silk on which to 

 rest. The actual process of moulting occupies about three or four minutes. 

 The head of the larva is forced through the old skin immediately behind the 

 head-capsule so that the latter remains attached to the anterior ventral surface 

 of the head. The moulted skin is meanwhile forced back from the body by an 

 undulating forward movement. The larva then frees itself from the discarded 

 head-capsule by pressing it against the leaf surface while vigorously jerking 

 its head from side to side. The discarded skin remains grey and shrivelled,' 

 firmly attached to the leaf. As it invariably disappears a few hours after 

 moulting takes place it seems probable that the larva devours it. 



When nearing maturity the larvae often measure over 30 mm. (1J<£ inches) 

 in length and 4 mm. in width. They are dark green in colour, often showing a 

 tinge of blue; a narrow yellowish stripe extends mid-dorsally along the back, 

 and the spiracles are edged with yellow. Before pupation they cease to feed 

 and migrate in search of a favourable place to transform, rarely remaining on 

 the plants. Pupation takes place in sheltered nooks on fences, or under the 

 loose bark of trees, the larvae almost always exhibiting a tendency to ascend. 

 The larva spins a pad of silk to which it attaches its caudal end and a thread of 

 silk is also passed over the body about one-third of the distance from the head 

 and securely fastened at each side. The larva gradually becomes shorter and 

 thicker. Shortly after moulting the characteristic thoracic and abdominal 

 projections develop and pupation is complete. 



The chrysalids measure 18 mm. in length and 4 mm. in width. They vary 

 considerably in colour, apparently depending somewhat on the colour of the 

 object to which they are attached and to the amount of light to which they are 

 subsequently exposed. Overwintering chrysalids found on exposed surfaces 

 were pale yellowish gray, whereas those taken from dark situations were dark 

 brown. Summer generation chrysalids on the leaves of cabbage are usually a 

 bright green in colour, the thoracic and abdominal projections being yellow 

 tinged with mauve. Rarely they were found coloured pale mauve tinged with 

 yellowish green. Twenty-four hours before the imago emerges the wing pads 

 become bright yellow and the black wing markings of the adult can be clearly 

 seen. 



