16 PRACTICAL ZOOLOGY. 



in most insects. Note the effect of removing the 

 balancers. 



4. The wings describe a figure 8 in flying, and make over 

 300 revolutions (i.e., go up 300 times and down 300 

 times) in a second. 



5. On each side of the thorax, just back of the head, find 

 a narrow opening with yellow, lip-like border ; ex- 

 amine closely with the aid of lens and microscope. 

 It is a breathing pore, or spiracle. 



THE ABDOMEN. 



Are there spiracles on the abdomen ? How many rings 

 has the abdomen? Draw the fly as seen from above, 

 dorsal view. 



The house fly lays its eggs about stables ; after a day or 

 two the eggs hatch out as little worms, or maggots, which 

 eat voraciously and grow rapidly ; in about a week they 

 cease eating, become dry and brown, resemble a seed, and 

 neither move nor grow ; from this pupa the fly emerges. 

 The adult fly is short lived, though some live over winter. 

 Watch the development of the egg which the flesh fly lays 

 on meat and dead animals. How many kinds of flies do 

 you know ? How do they differ ? How does the fly walk 

 on the window pane ? Examine the feet. In what order 

 does the fly move its feet in walking ? For the study of 

 this point, take a fly that is sluggish from cold, or from 

 partial drowning. Do flies, on the whole, injure man, or 

 benefit him? Flies belong to the order Diptera, or two- 

 winged insects. What other insects have but two wings ? 

 Head the Muscidse in Packard's " Guide to the Study of 

 Insects." 



