THE TSETSE FLY 31 



the sleeping sickness parasite, and also that in the 

 laboratory experiments, when flies were fed on infected 

 animals, in about 92 to 95 per cent, of the infected 

 flies the trypanosomes died out completely, and the 

 germ carriers became harmless again. A point worth 

 noting in connexion with these experiments was 

 that when a fly was interrupted in its feed from an 

 infected animal, it was infective to a clean animal 

 on which it next fed. The possibilities of repeated 

 infections by means of a single fly thus are exposed. 



The tsetse fly that carries the deadly Trypanosoma 

 gambiense is not a very conspicuous object. Glossina 

 palpalis is slightly larger than an ordinary housefly, 

 and has a blackish-brown body. The under side of 

 the abdomen is pale, while the upper side cannot be 

 seen when the fly is at rest, as the brownish wings 

 close over one another, and lie flat on the back. 

 The head has a very prominent proboscis. The 

 tsetse fly does not lay eggs, but within her body a 

 yellowish, footless maggot develops. When this is 

 passed from the body of the parent, it creeps into 

 the soil, and becomes dark in colour. In hot 

 weather the perfect fly may emerge from the pupa 

 case in seventeen days, but should the weather be 

 cold, as long as two and a half months may elapse 

 between the pupation and the emergence of the fly. 

 One female produces eight or nine young successively, 

 and no more. 



In connexion with the transference of the disease 

 a few points in the habits of the Glossina may be 

 noted. In the first place the diet of the tsetses 

 does not consist solely of human blood ; in fact, 



