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infections, these long-slender promastigotes were seen swimming in the 

 anterior portion of the abdominal midgut, cardia and hind triangle 

 (Fig. 4-5). They measured about 12 and 2 ym in length and width, 

 respectively, with a flagellum as long as or longer than the body. 

 Intermediate forms between the ovoid and long-slender promastigotes 

 were al so observed. 



Three-day-old infections were characterized by tremendous numbers 

 of long-slender, highly motile promastigotes packed in the abdominal 

 midgut, with anterior migration to the. cardia, where shorter and 

 broader dividing forms were seen attached to the stomodeal valve (Fig. 

 4-4e). These broad dividing forms measured 5-6 and 2-3 ym in length 

 and width, respectively, with the flagellum equal in length to the 

 body. The smaller dividing forms seen on days one and two were 

 present in lesser numbers in the abdominal midgut on day three. In 

 dissections where the alimentary tract was still intact, the parasites 

 were packed in so tightly that the gut was noticably swollen and 

 movement of parasites was restricted to stationary flagellar 

 undulations. When the gut wall was ruptured, parasites spewed into 

 the dissecting medium as if under pressure (Fig. 4-6). Masses of 

 them appeared to be joined together by a gel-like matrix. In only one 

 fly each, of three-day infected Lu. diabol ica and Lu_. shannoni the 

 parasites had advanced beyond the stomodeal valve and into the 

 esophagus, gaining entry into the pharynx and mouthparts (Tables 4-2 

 and 4-3). In addition, small numbers of long-slender promastigotes 

 were seen swimming freely in the hind triangle and throughout the 

 hindgut to the rectal ampullae (Fig. 4-5). 



