ARTHROPOD A 



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gled in the hairs and folds of its proboscis, wings or legs. The wings of. 

 a fly when examined under moderate powers of the microscope are found 

 to be covered with thousands of tiny, stiff hairs, too small to show in 

 the figures here represented, and the legs are covered with numerous 

 larger hairs as shown in Fig. 72. In the dirt (see Fig. 71) that collects 

 among these hairs is room for millions of bacteria, so that in a series of 



FIG. 73. Eggs of the house-fly. X i . (From Howard, House Flies, after Newstead.) 



experiments it was found that on an average a single fly may carry about 

 1,250,000 bacteria; these bacteria may be harmless but they are often 

 the germs of deadly diseases. Let such a fly crawl across a culture dish 

 and an astonishing trail of bacteria will develop along its course. 

 Where these bacteria are collected is easily understood when the breeding 



