82 



that given in the figure of 'A Tsetse-fly (Glossina morsitans), after 

 feeding,' in Austen's ' Handbook of the Tsetse-Flies ' on page 93. TSee 

 p. 81]. 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 chloro- 

 form and in this condition were weighed. They were then allowed to 

 recover consciousness, and when quite restored were fed undisturbed 

 on my fingers. .... 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 stupefaction produced by chloroform the process 



of digestion appeared to be arrested As the result of a 



number of such experiments the average weight of blood ingested by 

 the male was found to be -027 gm., which, reckoning the specific 



gravity of normal blood as 1-06, corresponds to 2-5 cmm 



The weight of the flies varies considerably with the length of time that 

 has elapsed since the last meal, but nevertheless there is an appreciable 

 difference between the weights of the unfed males and females. As a 

 rough average the unfed male weighs -020 gm., and the female, which 

 is somewhat larger, -028 gm., The same applies to the fed flies they 

 do not always engorge themselves to the same extent, but the average 

 weight of blood ingested is somewhat greater in the case of the female. 

 On one occasion as much as -0485 gm. (or 4-5 cmm.) of blood being 

 drawn up by a female, and -030 gm. by a male. The proportion is 

 perhaps better stated in comparison with the body weight a male 

 G. palpalis is capable of sucking up blood weighing 1 3 times his body 

 weight, and a female 1 -6 times her body weight. 



" With regard to the frequency with which the flies feed it was 

 generally found that once fed they refused to bite again until about 

 30 hours had elapsed. But here again the intensity of the last meali 

 has to be taken into account, for on one occasion a fly which had fed 

 very fully refused to feed again until 70 hours later. As the flies were 

 all confined in glass jars containing no water this shows that when 

 fully and naturally fed they are able to live unfed much longer than the 

 30 hours that is sometimes given as the limit of their endurance under 

 such conditions. 



" Digestion. Having fed, the Tsetse-fly settles quietly to digest. 

 At first the under surface of the distended abdomen is uniformly red' 

 in the case of the male, but the female always has a pale opaque spot 

 at the distal end. In from two to five minutes, however, a pale bubble 

 appears at the proximal pole, situated generally just to the left of the 

 mid line. This bubble shows slight movements of contraction and 

 expansion, as though it were influenced by some peristaltic-like action 

 of the bowel, and moves gradually over towards the left side, keeping 

 all the time at the proximal extremity of the abdomen. On dissecting 

 a fly at this stage the bubble was found to be gaseous, and from the 

 fact that the red tint of the blood lingers along its edge long after it 

 has faded from the rest of the abdomen, we may surmise that it contains 

 oxygen as a constituent at any rate. Two other processes are mean- 

 while observed to be going on, namely, the exudation of drops of fluid 

 from the anus and a darkening of the ingested blood. 



" It is not until two or three minutes after the fly has settled down to 

 digest its meal that drops of fluid begin to be extruded from the anus. 

 The first drop is often, though not invariably, of a buff colour and 



