THE YOUNG INSECT 17 



are acquired gradually as growth proceeds, appearing first 

 as buds or rudiments from the second and third segments 

 of the thorax, and attaining their complete development 

 only after the final moult, when the insect becomes adult. 

 In the common cockroach the male alone possesses func- 

 tional wings, although in certain nearly related species 

 both sexes are capable of flight. 



The manner of growth exemplified in the life-history 

 of the cockroach obtains among many other insects, such 

 as crickets, grasshoppers, and earwigs, while there is good 

 reason for thinking that the ancestors of all insects reached 

 maturity in this way. At the present day, however, a vast 

 number of insects undergo a much more elaborate process 

 of development. Their lives are mapped out into three 

 well-marked stages. Beetles, bees, wasps, ants, and butter- 

 flies are among the insects which undergo these transfor- 

 mations. Everyone knows, for example, that the young 

 butterfly — the caterpillar as we call it — differs in a thousand 

 ways from its parents. There is no family likeness what- 

 ever. Moreover, when a caterpillar has consumed its 

 allotted share of food, it does not immediately become 

 adult, but enters upon a more or less protracted period of 

 fasting and repose, when we call it a chrysalis. 



Let us examine a specific instance. When "the cater- 

 pillar of the silver-washed fritillary butterfly (Argynnis 

 paphia) has eaten its fill of violet leaves, it repairs to the 

 stem of some low bush, often a bramble, and there spins a 

 small pad of silk. This pad it grasps with its hindmost 

 pair of prolegs, and then lowers itself very deliberately 

 until it hangs head downwards. It remains thus, motion- 

 less, for some hours. Muscular contractions are then 

 noticeable, the skin splits dorsally, and is gradually 

 worked towards the tail by the efforts of the caterpillar, 

 which is now changing to a chrysalis before our eyes. 



B 



