66 HOW TO USE THE MICROSCOPE 



appear after some seven days in the chrysalis con- 

 dition. The perfect fly provides several interesting 

 features. There is its internal system, which must 

 be carefully dissected ; and, externally, we have the 

 large eyes formed of a great number of facets or 

 lenses, the antennae, the exceedingly wonderful 

 proboscis, and the spiracles, or air-openings, part of 

 the breathing system, in the body skin. Then we 

 have to consider the wings, and the legs, which are 

 covered with hairs and terminate in a pair of claws 

 and foot-pads, the latter enabling the fly to walk 

 easily upside down on the ceiling, or chmb up the 

 window-pane. There are other details to be exam- 

 ined. I have mentioned the foregoing as a rough 

 outline, and a general suggestion of the course 

 which a worker may follow. 



