THE H^MOFLAGBLLATES. 



157 



stantly beiug brouglit about by the never-ceasing, restless 

 activity of man. Witli tlie marcb of civilisation into the 

 " liiuterlands " of the various colonies, man, together with 

 the numerous domesticated animals which accompany him, is 

 brought into close proximity to big game and other wild ani- 

 mals, and, what is more important, into the zone of the par- 



FiG. 2. — Various blood-sucking flies. A and B. Glossina 

 morsitans (transmits the Trypanosome of Nagana, T. brucii) 

 X 2; 0, Hippobosca rufipes (thought to transmit the parasite 

 of *' Galziekte," T. theileri) X I5 ; D, Tabanus lineola (pro- 

 bably conveys the Surra parasite, T. evansi) X'll; E, Stomoxys 

 calcitrans (suspected in connection with T. equinum, of Mai 

 de Caderas [see, however, under Systematic] ) X 25. (a and B, 

 from Lave ran and Mesnil, after Bruce ; c, after L. and M. ; D and 

 E, after Salmon and Stiles.) 



ticular blood-sucking Insects which prey upon them. The new 

 arrivals thus render themselves liable to infection by parasites 

 to which they, unlike the indigenous animals of the neigli- 

 bourhoodj are quite unaccustomed. The new kind of host, 

 being, of course, totally unadjusted to the special environment 

 in which it finds itself and insufficiently supplied with reactive 

 or defensive powers, is unable either to exert a repellent in- 

 fluence on the parasite or to maintain a proper balance between 



