﻿OBSERVATIONS UPON GLOSSINA PALPALIS. 69 



It has been pointed out that movement plays a considerable part in attracting 

 the attention of tsetse-flies, and in his recent report on the Gambia, Dr. J. J. 

 Simpson has given several notable instances of this fact. But whilst it is 

 undoubtedly the case that movement does attract the flies from a distance, I 

 believe that at closer quarters some sense of smell is essential in guiding them. 

 In the glass jars in which I kept my flies, at any rate, as soon as a finger was 

 pressed against the gauze cover the flies came to feed, whereas they ignored any 

 other similar looking body, or even the leg or back of a guinea-pig in the same 

 position. Whether the body applied to the opening was moved about or kept 

 quite still seemed to make no difference. 



The Act of Feeding of Glossina Palpalis. 



The attitude during feeding is of course well known, the fly standing firmly on 

 all six feet and thrusting its honey-brown proboscis vertically downwards into the 

 skin, whilst the ensheathing palpi project forwards and upwards. As pointed out 

 by Dr. Moiser, the fly sometimes partially withdraws its proboscis and thrusts it 

 in again and again, but once a satisfactory well of blood has been tapped, the 

 abdomen fills rapidly and in from one to two minutes the act of feeding termi- 

 nates, and the fly, withdrawing its proboscis, moves to one side and presently 

 flies heavily away. 



In my experiments I have usually found the bite painless. Sometimes however 

 it was decidedly painful, and I can only account for this by supposing that on 

 these occasions the proboscis entered sufficiently near to one of the sensory spots 

 of the skin to stimulate it. On the other hand there was generally some degree 

 of smarting at the site of puncture after the feed was over, and it is probably 

 this which usually attracts the attention of the victim to the presence of 

 the fly, which having already fed is able to escape on the first indications of 

 uneasiness. 



If undisturbed, the fly feeds until the abdomen is relatively greatly distended 

 and of a bright red colour, due to the blood showing through the tense and semi- 

 transparent tissues. The dorsal plates of the abdomen are widely separated, so 

 that the body loses its characteristic dark colour. The appearance is therefore 

 somewhat different from that given in the figure of " A Tsetse fly ( Glossina 

 morsitans), after feeding " in Mr. Austen's " Handbook of the Tsetse flies " on 

 page 93. To determine the amount of blood actually drawn up, the following 

 experiments were carried out. Two or three tsetse-flies ( G. palpalis), that from 

 the almost linear dimensions of their abdomens had evidently not been fed for 

 some time, were stupefied with chloroform and in this condition were weighed. 

 They were then allowed to recover consciousness, and when quite restored were 

 fed undisturbed on my fingers. It was noticed that they almost invariably 

 selected the extensor aspect, a precaution that no doubt often saves them from 

 being crushed by a sudden flexion of the finger. They were once again stupefied 

 with chloroform and reweighed. The difference between the two weighings^ 

 represented the weight of the blood taken up, for sufficient time was not allowed 

 to elapse after the feeding for any exudations to be lost, and in the condition of 



