THE ANIMAL KINGDOM. 



95 



the weight of its poison apparatus by means of the most 

 delicate balance, we should perhaps find the calculation 

 impossible on account of its smallness. 



It is an inexplicable anomaly that this fly, which inevita- 

 bly kills certain animals, does not injure others. It selects 

 all its victims from our cattle ; the goat and the ass alone 

 defy its sting. Nor do its attacks produce any effect upon 

 man and wild animals. But what is still more singular, this 



44. The Tsetse Fly. a, Natural size; b, magnified; c, proboscis magnified. 



dipterous insect kills the adult animal, but sucks the blood 

 of its offspring without doing any mischief. The tsetse 

 quickly poisons the full-grown ox, but produces no effect 

 upon the calf. Livingstone says that during his wanderings 

 his children were frequently stung by it, without ever suf- 

 fering in the least degree ; in fact, they paid no attention 

 to it ; whilst the deadly fly killed forty-three oxen in spite 

 of the strictest watch. 



