PARASITISM 



329 



leaf-hoppers (Homoptera), eating the sugary 

 and waxy secretions discharged by the hosts. 

 Order Diptera. This large order, the flies, 

 contains many representatives of strikingly 

 different appearance, whose mouth-parts are 

 fitted for sucking the juice of plants or the blood 

 of animals, either in the pupa or imago stages. 

 It also contains quite a number whose habits 



FIG. 115. Botfly in stomach of horse, also adult fly. (After Michener, 

 Report on Diseases of the Horse, U. S. Department of Agriculture, Bureau of 

 Animal Industry.) 



of ovulation are parasitic. A few forms are 

 obligatory external symbionts, as Melophagus 

 ovinus, the sheep tick. 



The flesh flies not infrequently lay their eggs 

 upon wounds and in discharging openings of 

 the bodies of animals where the maggots work 

 their way into the tissues. Though most 

 cases of myiasis seem to be by accident rather 



