66 Trypanosome Diseases of Domestic Animals in Nyasaland. 



slender, ribbon-like, very active trypanosomes, which in a former paper* were 

 called the normal reproductive type. By comparing Plate 7 with the insets 

 of that paper, the resemblance between the intestinal developmental forms of 

 T. simice and T. gambiense will be apparent. 



Conclusions. 



1. That T. simice can be transmitted from infected to healthy animals by 

 the tsetse fly G. morsitans. 



2. That T. simice multiplies in the intestines and in the labial cavity of the 

 proboscis of the " fly." Here only developmental forms are found, never 

 infective forms. 



3. That the T. simice growing in the intestines of the " fly " has no specific 

 characters by which it can be distinguished from other species of pathogenic 

 trypanosomes found in tsetse flies. 



4. That the final stage of the development takes place in the hypopharynx, 

 wherein the infective form of the parasite, similar in shape to the trypano- 

 some found in the blood of infected animals, is produced. 



5. That the flies do not become infective until about 20 days after their 

 first infected feed. 



DESCRIPTION OF PLATES. 

 Plate 6. 



Fig. 1. — Appearance of the labial cavity of the proboscis of Glossina morsitans with 



Trypanosoma simia; growing in clusters attached by their flagellar extremities to the 



inner surface of the labrum. Living and unstained, x 500. 

 Fig. 2. — Appearance of the hypopharynx in the same fly, showing innumerable small and 



active T. simice almost blocking up the lumen of the duct. Living and unstained, 



x500. 



Plate 7. 



Intestinal developmental forms of T. simia;. These do not differ in appearance from the 

 developmental forms of other species of pathogenic trypanosomes found in the 

 intestinal tract of tsetse flies. 



Plate 8. 



Developmental forms of T. simia; from the labial cavity and hypopharynx of G. morsitans. 



Figs. 1-11. — Trypanosomes ejected by a living G. morsitans on attempting to feed 

 through a cover-glass. These are supposed to be intestinal forms pressed up into 

 the proboscis and on to the glass by the muscular contraction of the fly. 



Figs. 12-16. — T. simia' growing in the labial cavity of the proboscis of G. morsitans. 



Fig. 17. — Aberrant form from hypopharynx. 



Figs. 18-29. — Blood forms of T. simia; found in the hypopharynx. These form the final 

 stage in the developmental cycle of this species of trypanosome and are the only 

 infective forms. Stained Giemsa, x 2000. 



* 'Roy. Soc. Proc.,' 1911, B, vol. 83, p. 513. 



