3 20 TEXT-BOOK OF ZOOLOGY 



five other pairs — the so-called abdominal or pro-legs — are developed. 

 These are, in fact, saccular cutaneous tubercles attached to the third, 

 fourth, fifth, sixth, and last (where they are known as the " claspers ") 

 of the abdominal segments. Their lower surfaces, or " soles," are usually 

 bilobed and furnished at the margins with numerous small hooks, by 

 which they are adapted for climbing and holding fast to objects. LarvsB 

 with at most five pairs of pro-legs are called " caterpillars." (Contrast 

 with these the so-called false caterpillars of sawflies.) 



5. Since the larva lives on solid food, it possesses masticatory organs. 

 The mandibles form powerful masticatory pincers. 



6. These pincers require strong muscles to set them in action, and 

 the muscles in their turn must have firm points of attachment. These 

 latter are provided in the chitinous skeleton of the head, which accord- 

 ingly is very hard and firm as compared with the rest of the body- 

 covering. 



7. Like the majority of animals living above ground, the larva 

 possesses eyes. Six of these are situated on each side of the head, and 

 they are of the form of " simple eyes," ocelli or stemmata (see p. 317). 

 The antenna are very minute structures. 



8. Its colour (bluish-green, with black dots and a yellow stripe on 

 the back and on each side) renders the larva hard to distinguish on the 

 bluish-green cabbage leaf, especially when it clings tightly against one 

 of the veins of the leaf. But in spite of this protective colouring the 

 larva is easily discovered by its most dreaded enemy, the ichneumon fly 

 (which see). Birds mostly despise it, probably on account of the green 

 fluid which the insect vomits when touched. Man, however, pursues it 

 with unmitigated zeal for spoiling the fruits of his industry. Anyone 

 who has seen a cabbage field with only the naked ribs of the leaves 

 left standing will at once recognise the damage wrought by this insect 

 pest. Naturally, the best way of stamping it out would be to kill the 

 butterflies before they deposit their eggs. This, however, is very difficult. 

 But some good may be done by crushing the eggs and young larvse while 

 they are still crowded together, as well as by industriously picking off 

 the older larvse and by carefully protecting the pupse of the ichneumon 

 flies. 



C. Pupa. 



1. By the time the larva has attained to its full size and laid up a 

 requisite store of food material within its body, it enters upon its pupal 

 condition. By this time, however, the food plants, with few exceptions 

 (e.g., the red cabbage), have been killed off by the winter cold, and are 

 covered with snow and sodden with water. They would in this con- 



