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 
ora 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 
larve 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, 
