PARASITES THAT ARE FREE WHEN OLD. 178 



little. Their presence can at most only cause some 

 uneasiness, or some trifling functional trouble. 



The cestri are dipterous like ordinary flies ; but 

 instead of passing their youth on some waste organic 

 matter, they live in the nostrils or the stomach of some 

 hairy animal, and undergo all their metamorphoses in 

 the interior of its body. 



Thus they pass all their youth in a creche ; but when 

 they have reached the adult state, they get their own 

 living in freedom. 



These cestri especially attack herbivorous mammals, 

 and the terms gastricola, cuticola, and cavicola, suffi- 

 ciently indicate the places which they inhabit ; the first 

 kind lodging in the stomach, the second frequenting the 

 skin, and the third establishing themselves in some of 

 the cavities of the body. 



Dr. Livingstone doubtless alludes to some kinds of 

 cestri when he mentioned the numerous intestinal worms 

 which infest animals in Southern Africa : 



" All the wild animals," says the celebrated traveller, 

 "are subject to intestinal worms. I have observed 

 bunches of a tape-like thread-worm and short worms 

 of enlarged sizes in the rhinoceros. The zebras and 

 elephants are seldom without them, and a thread-worm 

 may often be seen under the peritoneum of these 

 animals. Short red larva, which convey a stinging sen- 

 sation to the hand, are seen clustering round the trachea 

 of this animal, at the back of the throat ; others are 

 seen in the frontal sinus of antelopes ; and curious flat 

 ]eech-like worms are found in the stomachs of leches " 

 (a new species of antelope).* 



• Missionary Travels in South Africa, p. 136. 



