6 FIRST LESSONS IN ZOOLOGY 



The tense surface film holds the little mass together in 

 the form of a drop. The mosquito larva takes advantage 

 of the surface film and is able to keep itself at the surface 

 when breathing by hanginj.'^ from it. Water-striders and 

 the numerous little flies which run quickly and safely 

 about on the surface of the water are supported by the 

 film. Their feet make little dents or depressions on the 

 water's surface, but do not break through. 



It is probable that the movements of the feeding-brushes 

 also help to keep the wriggler at the surface, as the 

 wrigglers seem to be able to balance themselves, i.e., 

 keep from sinking, in the water by these movements. 



Observing the larva; or "wrigglers " from day to day 

 it will be noted that the}' increase in size, that is, are 

 growing. They breathe and feed and swim and grow. 

 And some keenly observant pupil may see that they 

 occasionally cast their skin, or moult. That the larvae 

 do moult one or more times is certain ; how many times, 

 however, has not yet been found out. 



The pupae. — After several days — ^just how many each 

 pupil should determine for himself — the long slender 

 larv;u enter upon another stage in the mosquito's life 

 called the ptipal stage, and the young mosquitoes are now 

 called pupcc. In this stage the head end is large and 

 bulbous, the hind body is usually curled underneath the 

 head, and the creature spends most of its time floating at 

 the surface. It can swim, and docs so when disturbed, 

 by a peculiar straightening and folding of its body. 

 When it stops swimming what happens to it 1 In what 

 way must the pupa differ from the larva in its relation to 

 the density of water .'' 



Examine with a hand lens one of the pupaj in a watch- 

 glass of \\ater. Note the two tubes or horns which 

 project upwards from the back or dorsal part of the 

 bulbous head end of the bodj^ and the pair of flaps at 



