504 FAMILY: TRYPANOSOMID^ 



the hind-gut, and that the development is one in the posterior station, as 

 in the case of T. lewisi in the flea (Fig. 213). The many observers who 

 regarded the ked flagellate as peculiar to the insect have described encysted 

 forms in the rectum, and it was supposed that these were ingested by other 

 keds, which consequently became infected. That such an infection did not 

 take place was proved by Kleine (1919a), who found that uninfected keds 

 hatched from pupse in the laboratory did not become infected when kept 

 with keds already infected. He showed, furthermore, that uninfected 

 keds did not become infected when fed on goats which did not harbour 

 trypanosomes. It is evident, therefore, that the bodies described as 

 cysts in the faeces of the keds by various observers who have investigated 





> 



® ® ^ §,. - -^ 



'mm 





Fig. 214. — Structures in the Hind-Gut of the Ked, which might be Inter- 

 preted AS Cysts of Flagellates (x 2,000). (After Hoare, 1923.) 



1. Accumulation of staining material round a flagellate producing appearance of a 

 homogeneous cyst wall. 2-5. Stained granular debris round leishmania forms. 



G. Deposit round short flagellate form. 7-8. Yeasts of the Cryptococcus type. 



9. Metacyclic trypanosome superimirosed on a yeast. 10-12. Yeasts in various stages. 



this flagellate were not of this nature. They were in many cases leish- 

 mania forms round which deposits of stain had taken place, or even other 

 organisms, such as yeasts (Fig. 214). It is possible that the cysts Avhich 

 have been described in the case of H. grayi of tsetse flies may be of a 

 similar nature. The cycle of development of the ked flagellate, as de- 

 scribed by Porter (1910), in which the various phases (pre-flagellate, 

 flagellate, and post-flagellate) occur are quite erroneous. The work of 

 Hoare has finally established the identity of the ked flagellate and the 

 trypanosome of sheep, and, furthermore, shows that many of the Crithidia 

 of blood-sucking arthropods require reinvestigation from the point of view 

 of their possible relationship to vertebrate trypanosomes. T. melophagiimi 



