36 



INSECT LIFE. 



LESSON XIV. 



MOLTING. 



1. Take a locust that has been killed by being 

 placed in a cyanide bottle or in alcohol and cut the 

 abdomen in two, near the middle of it. 



2. Observe that the hard parts of the body are on 

 the outside, and that there is no internal skeleton, as 

 in our own bodies. 



This fact makes necessary a peculiar feature in 

 the growth of insects and of the other animals that 

 are closely related to them. The 

 body of an insect is inclosed in a 

 firm case, which, as it does not in- 

 crease in size, becomes too tight for 

 the insect as the insect grows. To 

 meet this difficulty the outer hard 

 layer of the skin is shed. The inner 

 soft layer of the skin then stretches 

 so as to accommodate the increased 

 size of the insect ; later this soft 

 skin, which is now on the outside, 

 becomes hard, so as to serve as a 

 protection to the insect. In time 

 this skin also becomes too tight, but 

 another soft skin has been formed 

 beneath it, and the hard skin can be 

 shed like the other. 

 This process of shedding the skin is termed 

 molting. 



Insects differ greatly as to the number of times 

 that they molt ; some pass through only three or 



Fig. 17. — The cast 

 skin of a nymph 

 of a dragon-fly. 



