1910.] The Natural Food of Glossina palpalis. 



491 



smeared separately, and after staining (with one of the modifications of the 

 Komanowsky stain) were examined in the usual way. 



The dissections were carried out as follows : — The pharynx and proboscis 

 were removed with a needle, and having been placed under a cover-glass 

 and slightly opened out by pressure were examined in the fresh state. The 

 tube of the proboscis was in this way admirably displayed, and the presence 

 of red blood corpuscles or of flagellates could readily be determined. The 

 alimentary canal was then removed from the abdomen, and the salivary 

 glands detached from the fat-body. The alimentary canal was then 

 unravelled and laid out in its full length on a slide. The whole of the tube 

 ■could then be passed in review, from the junction of the thoracic intestine 

 with the fore-gut down to the rectum, and the contents at various levels 

 ileterniined, as far as possible, with medium power magnifications. The main 

 portions of the alimentary canal were then noted, and these were separated 

 from one another by cross cuts with a sharp-edged dissecting needle. In 

 this way the fore-gut, mid-gut, hind-gut, and proctodteum were separately 

 removed and smeared on a slide. The smears (whilst still moist) were 

 exposed to the vapour of osmic acid for a few seconds, and then passed 

 through alcohol before washing and staining. The proventriculus can, with 

 a little practice, be removed intact from the ventral aspect of the thorax. 

 If necessary, the thoracic portions of the salivary ducts can also be 

 recovered. 



Speaking in general terms, the contents of the various portions of the 

 alimentary canal could be determined with considerable accuracy from the 

 naked-eye appearance during dissection. If the fly has fed very recently, 

 the blood oozes from its proboscis when it is handled. The proventriculus, 

 the crop or sucking stomach, as well as the fore-gut, are greatly distended 

 with red blood. When the fed fly is put aside the blood-cells generally 

 •disappear from the proboscis in a few hours, though they may exceptionally 

 be found as long as 24 hours after a feed. Similarly, the proventriculus and 

 thoracic intestine quickly empty themselves, and the crop discharges its 

 contents into the upper alimentary canal within 24 hours. 



The blood travels slowly down the alimentary canal, changing in appear- 

 ance as it goes. The outline of the red cells can sometimes be distinguished 

 three days after a feed, but only when they have been retained in the fore- 

 gut. "When the blood reaches the mid-gut it begins to disintegrate and 

 becomes homogeneous and somewhat translucent ; when it reaches the lower 

 part of the mid-gut it first becomes dark and e^'entually black and tarry. 

 When in this state all cell elements are lost, and the colouring matter of 

 the red cells is recognisable in the form of amorphous black granules. When 



