58 THE INSECT WOKLD. 



face 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. Larvae of a Helophilus. 



It will be remarked that the body of each worm does not exceed 

 five lines in length. 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. Reaumur calls 

 it the breathing tube. It terminates in a little brown knob, in 

 which, according to Reaumur, 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 



