42 DRAGON flip:s vs. mosquitoes. 



house fly, the flesh fly, and the blow fly, with their thou- 

 sand allies, are doing something towards puritying the 

 pestilential air and averting the summer brood of cholera, 

 dijihtheria, and typhoid fevers which descend like harpies 

 upon the towns and cities. This useful species, to which 

 man owes more than he can readily estimate, and with 

 M'hich he can dispense only when the health of our cities 

 and towns is looked after with greater vigilance and intel- 

 ligence than is perhaps likely to be the case for several 

 centuries to come." 



As belonging less to life history and more to the do- 

 main of the medical question, we omit from this portion of 

 the essay all mention of such species of Diptera as Qi^strus, 

 Anthoniyia, et al., which are known to be inimical to the 

 health and comfort of man by reason of the hypodermic 

 or intestinal habits of their larvae. 



Several continental writers believe that the oily papillfe 

 which enable flies to adhere to smooth surfaces, are the 

 means of transporting disease. The fly's foot is illus- 

 trated Plate III., Fig. 4. 



III. 



LIFE HISTORIES AXD STRUCTURE OF THE 



ODOXATA. 



Ix approaching the life histories of the Odonata, we 

 find ourselves confronted with a more complicated series 

 of events, and a far more difficult problem to solve. 



AVliile the preparatory stages approximate those of the 

 CulicidfB, the imagos, on the other hand, are possessed of 

 habits which, on account of their powerful flight and wary 

 nature, are extremely hard to observe. 



