﻿62 DR. J. W. SCOTT MACFIE — EXPERIMENTS AND 



A note should perhaps be included here on the manner of death of the flies used 

 in the experiments. When an exposure was nearing a fatal termination the flies 

 became less active, and would presently settle on a twig, or on the floor of the jars 

 in which they were contained, in a lethargic condition, being with difficulty per- 

 suaded to move, even when touched with the end of a probe. A little later they 

 would fall over on to their backs with their legs pointing up into the air, and their 

 probosces projecting forwards. In this state they might remain for a considerable 

 time. At first, when disturbed, they would be able to struggle to their feet, only to 

 fall over on to their backs again in a few moments. Later they were only able to 

 respond by movements, more or less free, of the legs and proboscis. In this 

 condition, which in the notes of my experiments I have described by the 

 expression " as if dead," they remained until death took place, the movements 

 gradually becoming less perceptible. In exposures to an increased temperature 

 the flies sometimes spread out their wings convulsively just before death. After 

 death the proboscis was generally depressed. 



The Effect of a Lowering of the Temperature. 



In order to determine the effect of lowering the temperature on G. palpalis a 

 simple cold chamber was constructed by filling a large glass jar with ice and salt, 

 or ice and water, in which a smaller glass jar fitted with a thermometer was com- 

 pletely immersed. Into the smaller jar the fly was introduced together with some 

 leafy twigs on which it might alight. In such a chamber it was possible to watch 

 simultaneously the fluctuations of the temperature and the behaviour of the 

 imprisoned fly. 



As the minimum temperature recorded at Zungeru in 1910 was 57° F. 

 (13"8° C), a few experiments were at first carried out at temperatures of this 

 order. It was found, however, that with the exception that the flies became 

 somewhat sluggish, as if numbed, these temperatures had little effect. In one 

 experiment two male flies were exposed to 60-62° F. (15 , 5°-16 , 6° C.) for two 

 hours. On removal to the external air at 90° F. (32* 2° C.) they appeared to be 

 numbed and were with difficulty persuaded to move. Five minutes later, however, 

 they were quite lively and actively flying about. 



The effect of lower temperatures was then examined. The following are the 

 notes of one of the experiments : — 



No. 1. — One male and one female G. palpalis. Temperature of the 

 external air— 24° C. (75'2° F.). 



8.5 p.m. T. 12° C. Flies introduced into the cold chamber. 

 8.8 T. 11 Male fell to the ground "as if dead." Female 



still active. 



8.10 T. 10 Female resting on a twig. 



8.11 T. 8 Female fell to the ground " as if dead." 



Both flies were then removed to a box at the temperature of the external air. 

 The female recovered activity immediately, but the male only after a little time, 

 and was unable to fly until 8.20 p.m. — 9 minutes later. 



