198 INSECTS 
or other features gradually develop. It is very rare indeed 
for the young to have quite the same form as the adult, as 
is the case in higher animals. 
Molting. — The outside of the insect is a comparatively 
hard, tough substance, and corresponds to the skeleton which 
the higher animals have internally. This skin or shell does 
not stretch much, and as the animal grows it soon becomes 
too small; in due time another skin forms underneath, and 
‘finally the old one splits open and comes off. This process 
is called molting. Some insects molt only three 
or four times during their growth, while others shed 
their skin twenty times or more before they attain 
their full size. 
The Adult. — The following facts about adult 
insects are of interest : 
(a) The large majority of insects in this state 
have wings, though there are many exceptions. 
(b) An insect never grows after it has reached 
Castorr this stage. Small flies, for example, do not grow 
Skin or into large flies. The adult insect therefore does not 
YouNG 
Locust molt. 
(c) Many adults eat -more or less, but only to 
sustain life, not to grow. Indeed, some of them take very 
little food, while certain ones have no mouth parts at all. 
In some classes of insects, however, as in the grasshoppers 
and potato beetles, the adults as well as the young are raven- 
ous eaters. 
(d) The adult stage usually lasts a shorter time than the 
larva stage. In fact, the usual plan is that the mature in- 
sect shall live only long enough to lay eggs and thus secure 
the perpetuation of the species. Counting the whole period 
from the laying of the egg to the death of the adult, a year 
