ARTHROPODS. CLASS INSECTS 



127 



In the flies, beetles, butterflies, and numerous insects 

 the differences between the newly hatched young and the 

 adult are vastly greater. No one looking on a caterpillar 

 or a grub for the first time would suspect its origin, and 

 the changes they undergo have attracted attention for cen- 

 turies. Placing any of the ordinary caterpillars with their 

 favorite food in a glass-covered box, we may readily watch 

 their transformations. Provided with biting mouth-parts 

 and a voracious appetite, they devour vast quantities of 

 vegetation for several days. Finally they cease eating, and 



FIG. 79. Life-history of silk-moth (Bombyx mori). A, adult ; B, C, D, caterpillars of 

 different ages ; E, F, G, silken cocoon and pupa ; H, eggs. 



suspend themselves head downward by means of a kind of 

 cobweb. After remaining quiet a few hours, they burst 

 their skin, and within appears a chrysalis or pupa. In the 

 moths, for example, the silk-moth (Fig. 79), the caterpillar 

 or silk-worm, after eating the favorite mulberry leaves, 

 spins a silken cocoon, in which the pupa is produced. The 

 larvae of beetles and many other insects excavate tunnels in 

 wood or in the earth, and there undergo their transforma- 

 tions. Invariably the pupa remains quiet for days, months, 

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