ISO 



MANUAL OF ELEMENTARY ZOOLOGl 



tsetse fly, G. morsitans, which spreads another trypano- 

 some, T. brucei, the cause of the South African cattle 

 disease. Glossina sucks the blood of various backboned 

 animals — cattle, antelopes, birds, and so forth, as well as 

 man — and thus takes into its stomach such parasites as may 

 infest the blood vessels of its victims. When the object of 

 the attack of G. palpalis is infected with the trypanosome 

 of sleeping-sickness, the insect becomes capable of inocu- 

 lating a new host in the course of its feeding. The power 

 of inoculation is soon lost, but is regained after about 

 twenty days. It seems probable*that the first inoculations 



Fig. 92. — The tsetse fly Glossina palpalis. — From Thomson. 



are made with trypanosomes which are still fresh in the 

 proboscis of the insect, but the later ones with individuals 

 which arise from the stumpy forms after passing through 

 a course of development in the insect's alimentary canal 

 and salivary glands. During this development the stumpy 

 forms become first long and slender, then, attached to the 

 wall of the salivary gland, pass through a " crithidial phase " 

 in which the membrane starts in front of the nucleus, and 

 finally as stout-bodied, mature individuals are injected with 

 the saliva when a new victim is bitten. 



Besides those that we have mentioned, there are known 



