DIPTERA. 225 



More familiar are the mosquitoes, which lay their eggs on 

 stagnant water. The larvae hatch out and are known as 

 "wrigglers." They pupate beneath the surface, and 

 finally the perfect insect emerges to make itself an unmit- 

 igated nuisance about our persons. Many proposals have 

 been made for reducing the number of these torments. 

 The best is, possibly, the pouring of kerosene upon the 

 surface of all stagnant water. This will kill the eggs as 

 they are laid, while it also destroys the perfect insects as 

 they come from the water. 



COMPARISONS. 



With two columns, one for grasshopper, beetle, squash- 

 bug, and butterfly, the other for crayfish and sow-bug, 

 answer the following questions : 



(1) Is the body made up of a series of segments ? 



(2) Do any of the segments have jointed appendages ? 



(3) Do you find more than one pair of appendages on one 

 segment ? 



(4) Are the hard parts (skeleton) external or internal ? 



(5) Do the jaws work in a vertical or in a lateral plane ? 



(6) Can the jaws be compared to the other appendages of 

 the body ? 



(7) Is the heart above or below the alimentary canal ? 



(8) Is the brain above or below the oesophagus ? 



(9) Where is the largest part of the nervous system ? 



(10) Is there any relationship between nerve-enlargements 

 (ganglia) and the external segments of the body ? 



