DIPTERA. 



69 



distant, was entirely free from the pests. This was the more singular that we 

 often saw natives carrying over raw meat with many tsetse upon it. This insect 

 is not much larger than the common house-fly, and is nearly of the same brown 

 colour as the honey-bee. The after part of the body has three or four yellow 

 bars across it. It is remarkably alert, and evades dexterously all attempts to 

 capture it with the hand at common temperatures. In the cool of the mornings 

 and evenings it is less agile. Its peculiar buzz when once heard can never be 

 forgotten by the travellers whose means of locomotion are domestic animals, for 

 its bite is death to the ox, horse, and dog. In this journey, though we watched the 

 animals carefully, and believe that not a score of flies were ever upon them, they 

 destroyed forty-three fine oxen. A most remarkable feature is the perfect harmless- 

 ness of the bite to man and wild animals, and even calves so long as they con- 

 tinue to suck the cows, though it is no protection to the dog to feed him on milk. 

 The poison does not seem to be injected by a sting, or by ova placed beneath the 



tsetse fly (enlarged). 

 a, Side view of head ; b, Antenna. 



skin, for, when the insect is allowed to feed freely on the hand, it inserts the 

 middle prong of the three portions into which the proboscis divides somewhat deeply 

 into the true skin. It then draws the prong out a little way, and it assumes a ; 

 crimson colour as the mandibles come into brisk operation. The previously 

 shrunken belly swells out, and, if left undisturbed, the fly quietly departs when it 

 is full. A slight itching irritation follows the bite. In the ox the immediate 

 effects are no greater than in man ; but a few days afterwards the eyes and nose 

 begin to run, the coat stares, a swelling appears under the jaw, and sometimes at 

 the navel ; and though the poor creature continues to graze, emaciation commences, 

 accompanied with a peculiar flaccidity of the muscles. This proceeds unchecked 

 until, perhaps months afterwards, purging comes on, and the victim dies in a state 

 of extreme exhaustion. The animals which are in good condition often perish 

 soon after the bite is inflicted with staggering and blindness, as if the brain were 

 affected. Sudden changes of temperature produced by falls of rain seem to hasten 

 the progress of the complaint, but, in general, the wasting goes on for months. 

 When the carcase is opened, the cellular tissue beneath the skin is found injected 

 with air, as if a quantity of soap-bubbles were scattered over it. The blood is 

 small in quantity, and scarcely stains the hands in dissection. The fat is of a 



