54 DRAGON FLIES VS. MOSQUITOES. 



Grassi's experiments consisted principally in placing the 

 eggs of a human Nematoid (tape worm) parasite on a 

 plate, from which the flies sucked them up, for they w^ere 

 found in the excreta spots on sheets of white paper hung 

 up for that purpose. The same results were obtained with 

 the ripe segments of Taenia solium, another tape worm. 



" E. P. AV.,"^^^ reviewing the discoveries and speaking 

 of the fly's food, says : " It may be the expectoration of a 

 phthisical or the ejecta of a typhoid patient, but, irre- 

 spective of the material, their next visit may be to the 

 moist lips or eyes of a human being." He adds : " It 

 seems scarcely doubtful that in Egypt ophthalmia is con- 

 stantly carried by such winged visitors." Taylor,^'^*^ Gi- 

 rard,"*^ and Leidy ^^ record instances in which flies have 

 spread gangrene and other diseases. 



We may dismiss Musca domestica with a plea in its be- 

 half, that as a well known scavenger it is far too useful 

 to man to warrant its extermination without mature de- 

 liberation. 



Leaving the sucking group and coming to the biters, we 

 have to deal with a very different state of things. 



Stomoxys calcitrans is the species of the biters which 

 is most frequently taken for Domestica, as it is a common 

 visitor in our houses. It is referred to on page 40, and 

 its proboscis is illustrated on Plate IV., Fig. 4. Riley and 

 Howard ^^^ bear testimony to its powers as a biter. Akin 

 to it is the recently imported horn fly, Haematobia serrata 

 (Plate IV., Fig. 1), which has been quite common in houses 

 during the rainy season this fall ; we apprehend that it 

 will soon be one of our " house flies." 



Anthrax, or malignant pustule, a disease much dreaded 

 in certain countries, has, according to Macleay,^^ been 



