122 NATURAL HISTORY ESSAYS 



occur in Algeria, both in the region of the high 

 plateaux and in the actual Sahara ; vast natural 

 depressions, which may be either perfectly dry or 

 swimming with water — in fact, salt lakes.^ Pans occur 

 in many localities and climates; often thickly covered 

 with a three or four inch layer of coarse salt, they 

 offer in their sparkling surface a natural condiment 

 to man and beast. So fond of it are many animals 

 that it has been recorded that some duiker antelopes 

 kept in captivity without it bit off the heads of some 

 francolin "partridges " in order to obtain the saline 

 blood. On being supplied with salt the ante- 

 lopes let the francolins alone. The late Emin Pasha 

 used to explain this craving for salt by suggesting 

 that the animals by swallowing it were enabled to rid 

 themselves of internal parasites. At any rate, it is 

 well known that ruminant animals suffer largely from 

 the attacks of various intestinal worms, and the 

 pathological records of various zoological collections 

 show, only too frequently, disastrous results due to 

 the invasion of these puny agents. The Ascai'is 

 megacephala is a round worm which attacks not only 

 bears and wolves but also horses and zebras, though 

 it is said to be harmless to its involuntary hosts. Be 

 this as it may, Burchell's zebra is certainly injured by 

 some form or other of internal parasite, many having 

 recently been lost on an Uganda zebra farm from 



1 Renshaw: Natural History Essaj-s, pp. 174-175. A photograph of tlie 

 Cliott Tinsilt is also reproduced in the same work. 



