184 THE BOOK OF NATURE STUDY 



paint brush, the wing lying meanwhile on a moistened sheet 

 of glass ; (2) soak the wing in " eau de javelle " (hypochloride of 

 potash), after a preliminary dip into weak alcohol, an operation 

 which quickly removes all scales, but must be discontinued as 

 soon as these are off, and the whole wing will be rotted by the 

 liquid ; (3) steep the wing in benzene, and so render it transparent. 

 This last has the advantage of not injuring the specimen in any 

 way, for the benzene quickly evaporates and leaves no trace of 

 having been used. But with a little patience venation can 

 generally be made out without resorting to any of these methods, 

 especially if the under side of the wing be examined, for there the 

 veins are more prominent. 



Abdomen. The abdomen is almost black, and covered with 

 close hair-like scales. It probably consists of the usual ten 

 segments, but of these only eight are visible dorsally, and seven 

 ventrally in the male, and seven or six respectively in the female. 

 The remaining segments are invisible because they are withdrawn 

 inside the terminal segment, and greatly modified in connection 

 with the reproductive organs. Respiratory stigmata leading 

 into tracheal tubes are present on the sides of each of the visible 

 segments, except the first. Similar openings are also present in 

 the thorax, but there is doubt as to their number. 



Life-history. The eggs are to be found in May, and again in 

 late July and August. They are laid in patches of fifty to a 

 hundred or more upon the under (usually) side of the leaves of 

 cabbages and other cruciferous plants, and occasionally on 

 " Nasturtium " (Tropteolum) and Mignonette. The egg-shells 

 are flask shaped, delicately sculptured upon the surface, and 

 waterproof. The young caterpillars emerge about ten days 

 after the eggs have been laid, biting their way through the shell 

 with their strong mandibles, and in a short time set to work 

 devouring the substance of the leaf. They feed ravenously and 

 grow rapidly, moulting their skins four or sometimes five times as 

 the exo-skeleton becomes too small for the growing internal organs. 

 Prior to each moult a small carpet of silk is spun over a portion 

 of the leaf, and upon this the larva rests, obtaining a firm foothold 

 and anchorage for the husk shortly to be abandoned. The full- 

 grown caterpillar is about 2\ inches in length, and, as it differs 



