Trypanosome Diseases of Domestic Animals in Nyasaland. 59 



1\\ all three groups the common factor which leads to the formation or 

 development of the final or infective forms is the invasion of the salivary 

 tract, and this is accompanied hy a reversion to the original blood forms. 



Definitions. 



In this paper the word " proboscis " will mean the piercing apparatus of 

 the " fly," made up of the labrum, labium, labellum, and hypopharynx. 

 There are two tubes in the proboscis : one for the passage inwards of blood, 

 made up by the coalition of the labrum and labium, the other for the passage 

 outwards of the salivary secretion — -the terminal salivary duct or hypo- 

 pharynx. The term " labial cavity " in this paper will mean the former, or 

 tube for conveyance of blood, the word " hypopharynx " the latter, or duct 

 for conveyance of saliva. In the past the use of the word " proboscis," 

 including both tubes, has given rise to a good deal of ambiguity. 



The definition of the words " infected " and " infective " were given in a 

 previous paper.* 



The term " blood form " means a stage in the development of the 

 trypanosomes in the " fly," when there is a reversion to the original form 

 found in the blood of animals, and from which the cycle of development 

 originated. 



The Development of T. simle in G. morsitans. 



Eight experiments were carried out with laboratory-bred flies. Two were 

 positive and six were negative. The following table shows these eight 

 experiments, the number of flies used, the number of infected flies found on 

 dissection and the number of days which elapsed before the flies became 

 infective : — 



Table I. 



Date. 



Expt. 



No. of 

 flies used. 



Experiment 

 positive or 

 negative. 



No. of infected 

 flies found. 



No. of days 

 before flies 

 became infective. 



1912. 













May 1 



502 



20 









June 27 



754 



31 



+ 



2 



50 



Oct. 9 



1477 



17 





1 





Nov. 11 



1582 



8 









„ 15 



1602 



20 









>. 21 



1622 



16 









1913. 













Feb. 5 



1847 



45 



+ 



7 



20? 



„ io 



1856 



16 









* ' Roy. Soc. Pioc.,' B, vol. 80. (" Infectivity of Glossina morsitans in Nyasaland.") 



