I METAMORPHOSES OF INSECTS 7 



After the operation, the creature is soft and 

 languid, and pauses to recover from its exertions. 

 Then it begins nibbling and devouring with increased 

 voracity, since its digestive organs are now more 

 capacious. Some insects make a fresh start with 

 their old skin, but many at once remove to new 

 feeding-grounds. Soon further enlargement necessi- 

 tates a second change. The moults* vary in frequency 

 in different species ; in general they occur about 

 three times, or oftener. Usually the first takes place 

 about the twelfth day, the second after the further 

 lapse of a week, the third happens six or eight days 

 later still, the power of consumption of food at each 

 moult being augmented. 



Sphinx ligustri, the Privet Hawk Moth, is known to 

 increase at the rate of over 11,000 times its original 

 weight in the space of thirty-two days, a pro- 

 portion, great as it is, largely exceeded by the 

 goat moth, which increases to the amount of no 

 less than 72,000 times its first weight, but this 

 larva is very long-lived. Reason for the immense 

 storage of food is found in the fact that all growth is 

 effected in the larva and pupa stages, for when the 

 insect becomes perfect it alters no more. The pupa* 

 period is not only a state of death-like sleep, during 

 which no food can be taken, it is the time when 

 occurs the most rapid development of the tissues of 

 the body. The nourishment accumulated by the 

 larva has to admit of these alterations, and has like- 

 wise perhaps to serve as an immediate source of 

 nutriment to the insect on its awakening at the end 

 of the important pupa season. 



