58 THE INSECT WORLD. 
of the water. He then increased the depth of the water by 
degrees; and as it got deeper, observed that the tail of each 
worm became longer. These tails, which at first were only two 
inches long, at last attained to five. 










































































































































































































































































































































































































































































































































































































































Fig. 40.—Larve of a Helophilus. 
It will be remarked that the body of each worm does not exceed 
five lines in leneth. The tail is a peculiar organ, by the aid of 
which the worm breathes, although its body may be covered by 
water to the depth of several inches. It is composed of two tubes, 
one of which shuts into the other, like a telescope. Réaumur calls 
it the breathing tube. It terminates in a little brown knob, in 
which, according to Réaumur, are two holes for the purpose of 
receiving the air, and which have five little tufts of hair, which float 
on the surface of the water. When the time comes for the meta- 
morphosis of these worms, they come out of the water and bury 
themselves in the earth; the skin then hardens and becomes a 
sort of cocoon. In this cocoon the insect loses the form of a 
worm, and takes by degrees that of the pupa, which it keeps until 
circumstances cause it to throw off its last coverings, and to appear 
in the winged state. . 
What an eventful life! what a life full of changes and turns of 
fortune is that of these insects, which pass the first and longest 
period of their existence under water, another part of their life 
