DISTRIBUTION OF OPHIDIANS. 20'.) 



waters or woods ; while the animals intended especially to 

 inhabit plains should be there found in abundance ; and 

 these views are confirmed by experience. We see in 

 Africa, instead of deer, many species of antelopes, wan- 

 dering in vast herds in open regions. S([uirrels are there 

 found in small numbers, and the species w^hich are there 

 met with generally depart from the true squirrels by their 

 terrestrial habits. The great number of the Rodentia that 

 people that continent almost all belong to terrestrial spe- 

 cies ; many of them even live in open countries, and, being 

 unprovided with means of defence, Nature has attended to 

 their preservation, by developing their organs of locomo- 

 tion, so as to make them true leapers ; and it is in this 

 manner that these animals possess the faculty of escaping, 

 by a sudden flight from the pursuit of their enemies. We 

 observe the same fact in certain mammifera of the insecti- 

 vorous order. — The Reptiles of that part of the world af- 

 ford still more striking examples of what we assert. 

 Africa alone supports a greater number of land tortoises 

 than all other parts of the world put together ; but the 

 fresh- water tortoises are in such small numbers, that wo 

 only know a single species of Emys, and possibly one or two 

 species of the genus Trionyx. Another observation worthy 

 of notice, is the small number of Batrachians proper to this 

 continent. There exist but a few toads, some species of 

 Bombinator, as many of the frog, and one or two species 

 of tree-frogs (Hyla.) The same fact presents itself as re- 

 gards tree and aquatic serpents. The Dryiophis and the 

 Homalopsis are entirely w^anting ; and there exists only 

 two species of the genus Dipsas, two of the Dendrophis, 

 and one or two of the Tropidonotus. The most striking 

 example, however, is the almost total absence of fish in the 

 fresh waters of Southern Africa. — But the general ob- 

 servations which we have made on the physical constitu- 

 tion of Africa cannot be applied to every country of that 

 part of the world. At the point of greatest breadth in 

 that continent, the great plateau w^hich occupies all the 

 southern part, descends rapidly towards the desert plains 

 of the north, and is prolonged, on one side, beyond the 

 Quorra, in Upper Soudan ; whilst the terraces of that same 



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