TRYPANOSOMA CONGOLENSE 



555 



a change into crithidia forms takes place, and these attach themselves to 

 the inner surface of the labrum, just as they do in the salivary glands in 

 the case of T. gambiense. It is from these crithidia forms that the final 

 infective metacyclic trypanosomes are evolved. 



Lloyd and Johnson (1924) find that during the early stages of develop- 

 ment the forms in the gut are short trypanosomes which are feebly 

 undulant and have no free flagellum (Fig. 228). There are then produced 

 long trypanosomes with free flagella, which migrate to the proventriculus 

 and thence to the labial cavity. These are difficult to distinguish" from 



Fig. 228. — Developmental Forms of T. congolense in Glossina tachinoides 

 (x 2,000). (After Lloyd and Johnson, 1924.) 



1-3. Forms in mid-gut. 4. Form in proventriculus. 



5-6. Forms from fixed colonies in labial cavity. 

 7-8. Pre-infective forms from labial cavity in hypopharynx. 

 9-10. Infective forms from hypopharjmx. 

 11. Infective form from hjrpopharynx of Glossina morsitans. 



the corresponding forms of T. gambiense or T. brucei. In the labial 

 cavity they become crithidia forms without flagella, and are attached in 

 compact colonies. The corresponding stages of T. vivax have flagella. 

 Subsequently slender crithidia forms, with the nuclei and kinetoplasts 

 close together at the posterior end of the body and with flagella, are 

 produced. These invade the hypopharynx and give rise to infective 

 forms, which resemble the trypanosomes of the blood in that there are 

 no flagella. In contrast to T. vivax infections the metacyclic trypano- 

 somes are numerous in the hypopharynx. 



