POSSIBILITIES AND COSTS. 59 



On the other hand, Leidy,^^ Pasteur/^^ Giard,"*^ Bessey,^ 

 Comstock/^ and many others have testified to the deadly 

 eifects of the various species of the Entomophthorse. 



All observers are familiar with the sight of a house 

 fly fastened to a window pane by a filmy fungus or cob- 

 webby growth, or with a caterpillar covered with little 

 vegetable growths, both members of this insect killing 

 group. Very little is known of the methods by which 

 insects may be made to inoculate each other with these 

 germs. Our own bibliography must not be taken as an 

 indication of the number of papers written on the sub- 

 ject, as we have only included a few representing epochs 

 in this research, and for additional literature we refer to 

 Forbes' ^^ most complete list. 



We regret that our experiments have been unproduc- 

 tive of anything new, and have contributed nothing to 

 set at rest the dispute as to their effectiveness. 



We believe that the propagation of such forms as at- 

 tack the house fly should receive more attention from ex- 

 perimenters ; that is, if the extermination of Musca do- 

 mestica is to be regarded as a wise move. 



Packard'"^ has pointed out that Nature's means of pre- 

 venting the too rapid increase of insect life is largely 

 through the medium of parasitic insects. There are sev- 

 eral insects which prey upon both families of Diptera 

 now under consideration, but none of them to such an 

 extent as do the various species of the Odonata. 



The preparatory stages of the Culicidse and INIuscida) 

 are passed under such widely diverse conditions, the 

 Odonata will have to be considered under different heads. 



There are other problems yet untouched by investi- 

 gators. Prominent among them is that of solar physics, 



