132 



INSECT LIFE. 



ilar places. There are two forms of them : one are 

 the larvae of mosquitoes, the other the pupas of the 

 same insects ; both are represented in Fig. 107. 



Collect some wrigglers and put them in a glass 

 of water where jou can observe them. This aquarium 

 should be kept covered when you are not studying 

 the insects in it. 



The Larv^ of Mosquitoes {School Work).— In 

 the study of wrigglers begin with 

 the larvae ; these are of the form 

 shown at a in Fig. 108. 



I. Note that when a larva is 

 at rest it hangs from the surface 

 with its head down ; several are 

 shown in this position in Fig. 107. 

 Fig. ic8.— Mosquitoes. 2. Notc that when a larva is 



a, larva; b. pupa. j* 4. u j "^ • • 1 



*^ ^ disturbed it swims away with a 



wriggling motion or quietly sinks toward the bottom. 



3. Note that a larva can sink without any appar- 

 ent effort, while in order to regain the surface it is 

 forced to exert itself violently. Evidently the body 

 of the insect is heavier than water. 



4. Let us see if we can discover the means by 

 which the larva keeps itself at the surface without 

 any effort, although the body is heavier than water. 



Note that the true hind end of the body, the 

 last abdominal segment, is not at the surface, but is 

 turned to one side, and that what really reaches the 

 surface is the end of a tube borne by the next-to-the- 

 last segment. This is the breathing-tube of the 

 larva. If the pupil has the use of a microscope, a 

 larva should be mounted on a glass slip and the 

 structure of this breathing-tube examined. It will 



