CHEMICAL SENSITIVITY OF TARSI OF CERTAIN FLIES. 1 67 



its appendages carefully examined to determine their state of 

 perfection. If all six legs were not perfect, the animal was 

 usually discarded. If the legs were perfect, however, the wings 

 were cut off close to the body with fine scissors, and the animal 

 was mounted on a holder. The holder consisted of a straight 

 piece of telephone wire, 19 to 20 cm. in length, and flattened out 

 to form a small plate at one end. To this plate was attached a 

 rectangular block of beeswax deeply notched in the middle, thus 

 leaving two projecting tongues. By careful manipulation, it was 

 possible to heat the tongues one at a time with a hot needle, and 

 while the wax was still melted to attach the thorax of the fly to one 

 and the abdomen to the other, the entire operation being com- 

 pleted in about a minute. "Mounts" thus made are admirably 

 adapted for experimental work and make possible the rapid 

 handling of flies with the greatest ease (Fig. i). 



FIG. i. Side view of a mounted fly. b, block of beeswax notched at center; 

 w, wire flattened out at the end. 



Immediately after mounting, the legs of each animal were 

 carefully rinsed with distilled water to remove any foreign matter 

 adhering to them. Recovery from the anaesthesia usually re- 

 sulted in a few minutes, but a minimum period of two hours was 

 allowed from the time of anesthetization to the first trial. 



As far as could be determined without special experimentation, 

 mounting and experimentation failed, in the great majority of 

 cases at least, either to injure the animal or to shorten its life to 

 any appreciable extent. The animals were usually kept under 

 observation for at least 24 hours after the conclusion of the 

 experiment before being discarded. In one experiment, however, 

 involving eleven individuals belonging to the two species of 

 Phormia, the animals were kept on after the experiment until 



