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By the fourth day a massive infection was established in the 

 anterior cardia at the stomodeal valve (Fig. 4-7). The commonest 

 morphological form in this region was the broad dividing promastigote 

 (Fig. 4-4e). They were packed behind the stomodeal valve and were 

 attached to its surface by their flagella. When the anterior aspect 

 of the cardia was severed, they blossomed out into the saline, most of 

 them remaining attached to the cuticular surface of the valve (Fig. 

 4-8). Concomitantly, a heavy infection of long-slender, highly motile 

 promastigotes continued to remain in the abdominal midgut, with small 

 numbers appearing in the hindgut. In one four-day infection, 

 promastigotes were observed swimming in the diverticulum (crop). 



At five days, many parasites began to migrate beyond the stomodeal 

 valve, into the head, invading the esophagus, pharynx and mouthparts. 

 This anterior migration was accompanied by a reduction in size from 

 the larger broad forms to short-slender, highly active promastigotes. 

 These measured about 4-5 vm in length and 1-2 um in width. The flagellum 

 was longer than the body, measuring about 10 ym in length. 

 Although these tiny flagellates were observed as early as three days 

 in the mouthparts of a very few specimens, they were usually not 

 observed until the infection was at least five days old or older (Fig. 

 4-4f). Their movement was incredibly rapid and appeared to be random. 

 In a few six to ten-day infections they were observed throughout the 

 alimentary tract from the mouthparts to the ileum. In some five to 

 eight-day infections, nests of short-slender, highly active 

 promastigotes could be seen in the region of the stomodeal valve in 

 striking contrast to masses of larger, broader, sessile promastigotes 

 inhabiting the same area. In one five-day infection a long-slender 



