﻿OBSERVATIONS UPON GLOSSINA PALPALIS. 71 



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 

 meanwhile 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 2 or 3 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 turbid, but the succeeding 

 drops are of clear water-like fluid and are of the size of a pin's head. For about 

 20 minutes they are exuded at intervals varying from 15 to 75 seconds, the 

 intervals being somewhat longer towards the end of this period. Thereafter no 

 more drops are ejected for several hours, and those that follow are of a thick 

 chocolate brown excrement, which on microscopical examination is found to be 

 composed of little rounded bodies, staining a rich purple with Griemsa's solution, 

 and varying in size from mere dots to discs a third the size of a red blood 

 corpuscle. Around many a more or less disintegrated shell can be made out 

 which is probably the remains of an erythrocyte. Coincident with the extrusion 

 of these drops, which are presumably the fluid constituents of the blood, there 

 is a marked shrinking in the size of the abdomen. 



Soon after digestion has begun the appearance of the blood in the distended 

 abdomen of the fly begins to change. Commencing at the distal end and spreading 

 upwards the abdomen loses its bright red colour and gradually darkens, so that 

 in from 20 minutes to half an hour the last tint of red has gone. The last part 

 to darken is a narrow zone around the gaseous bubble, and as has been suggested 

 above, this may be due to the presence of free oxygen in it. 



Slight differences were observed in the case of the female G. palpalis. When 

 fully distended with blood her abdomen appeared to be deeper, or less dilated 

 laterally, than in the case of the male, and the process of darkening of the 

 ingested blood was considerably more rapid. In one case the last trace of red 

 colour had disappeared from the abdomen in 10 minutes. During the insensi- 

 bility induced by chloroform the processes of digestion seemed to be arrested, no 

 drops of fluid were exuded until consciousness began to return, and it was often 

 as long as an hour before the last tint of red had left the abdomen. The blood 

 in one fly dissected was found to be perfectly fluid half an hour after it had been 

 ingested. 



The Influence op Colour on Glossina Palpalis. 



Having previously ascertained that, in the case of the male G. palpalis confined 

 in a glass jar without water at a temperature of 40°-41° C. (104°-105 # 8° F.), whereas 

 exposure to direct sunlight was rapidly fatal, a similar result was only produced 

 after an hour's exposure if the jar was shaded from the direct rays by a covering 

 of thick brown paper, some experiments were carried out to determine whether 

 under similar conditions different colours would produce different results. Male 

 G. palpalis flies were therefore exposed to a temperature of 40°-41° C. in glass 

 jars shaded respectively with red, green, blue and yellow paper covers. No water 

 was present in the jars. In the case of the red, yellow and blue covers, after an 

 hour's exposure the flies seemed to be none the worse, and remained very active 



