182 HEUl'KTDMONAS rAG.*:i 



The flagelluin arises from this small dot or basal giaiiiile which, according to Minchin,' 



I >rigin of ougiit to be termed the blepharoplast. After its origin from the blepharoplast it occupies a 



median longitudnial position in tlie parasite and passes out of its anterior extremity as 



a tine tapering tilamentous structure, stained a deep red colour. It varies in length, 



and in adult flagellates it is about twice as long as the body of the parasite. 



Wlien tlie Hagellate reaches the adult stage, longitudinal division usually occurs aiul 

 two Hagellates result. Prior to division, enlargement of the tropho- and kinetonuclei 

 takes place, the latter becoming thickened and a constriction appearing in its middle. 

 A second small Hagelhiin, arising close to the original one, then makes its appearance, and 

 one is inclined to think that its origin is a separate one and that it is not due to a splitting 

 of the original flagellum. Many observations on hanging-drop preparations were made, but 

 it was iiii])ossible to come to any definite conclusion concerning this much debated point. 

 With the appearance of the second fiagellum the kiiietonucleus divides transversely into two 

 separate portions, and this is followed by a similar division of the trophouucleus. A line of 

 cleavage first forms between the sites of origin of the two flagella and extends in a posterior 

 direction along the body of the parasite ; when completed, two parasites result. These 

 again may undergo a second division, passing through more or less identical processes. The 

 parasite, therefore, multiplies by longitudinal division. Many observations were carried 

 out with hanging-drop preparations for the purpose of ascertaining whether conjugation ever 

 took place, but in no instance was this ever detected. In stained preparations one 

 was often inclined to think that parasites of different sexes were present. Frequently, large 

 stout forms measuring 30^ in length and 3^i in breadth and often devoid of a Hagellum were 

 present ; they were granular in structure and in Leishman-stained preparations it was 

 sometimes difficult to make out any differentiation between tropiionucleus and kiiietonucleus. 

 They stood out in marked contrast to the more attenuated typical forms of flagellates. 



In view of the fact, however, that conjugation was never observed, one must look 

 un these stout forms as degenerated parasites. 



Post -Flagellate Stage 

 Plate XL, tig. 16 



This is characterised in the first jilace by the herpetomonads becoming attached to 

 the lining epithelium of the colon, and if this portion of the gut be teased out on a 

 slide and stained, large masses of flagellates will be seen fixed to the gut wall by means 

 vst formation of their flagella, their posterior ends lying free. They appear to have undergone no change 

 in structure from the typical flagellates found in the mid-intestine and ileum, and in 

 order to study the various alterations occurring in the pai-asite prior to encystmeiit, 

 the following method was adopted : A large drop of fluid was taken from an emulsion 

 made up of the contents of the colon and placed on a glass slide ; a cover-glass 

 was then placed on this drop, and the margin of the cover slip ringed round with melted 

 paraffin so as to exclude the entrance of air ; a suitable hanging-drop preparation 

 was thus made, and no evaporation occurred. If such a preparation be examined, the 

 flagellates will be seen to show active movements for two or three hours. Several 

 things may happen ; the parasite may undergo longitudinal division once more, or, what 

 is more common, it becomes detached from the lining membrane of the gut and is a 

 free-moving flagellate. After two or three iiours its movements begin to get sluggish and 

 finally its position on the slide becomes a fixed one with only rhytiimical wave-like 

 contractions passing along from the posterior end to the flagellum. During these 



■ Mint-bin, K. A. (1908), " luvcstigatious ou the development uf Try pa nosouies in the Tsitse fly and 

 other Dipteni." Quarterly Joarnnl J/icrwtcojnc .Vcio«tv, Vol. LII., pp. 159-200. 



