375 



been observed in a Snake. If we add tbe fact that Snakes do not 

 produce many eggs or young ones, tliat they are aide to propagate 

 only when several years old, that they incur continual dangers by 

 their numerous enemies, and that tiny arc deprived of the in. an- of 

 performing distant journeys, we must consider it ;^ the natural con- 

 sequence, that no species will spread so tar as Batrachians. These 

 are enabled to endure temporary physical disadvantages, to traverse 

 localities without the regular supply for their lite, and to make up 

 yearly for the lost number by a numerous offspring. More or leal 

 confined to a thud element, they are favoured by another agency for 

 au easier spreading. But these facts are really "applicable to a com- 

 paratively small number of species only; and the question why we 

 do not find all these peculiarities equally exhibited in all the Batra- 

 chians or in a great part of them, is as difficult to be answered as 

 why one species is richer of individuals than the other: but it is 

 remarkable that just those species which are spread over the widest 

 range are also those distinguished by an intensity of individuals. 



On the other hand, we find Snakes almost entirely limited to the 

 original locality of the individual: but if the individuals are restricted 

 to the soil which gave them birth, the whole group, formed by such 

 individuals, is likewise stationary ; and if there be different creations, 

 corresponding to the different natural divisions of the earth's sur- 

 face, such a group as the Snakes must be best adapted for proving it, 

 because here the agencies are wanting by which a species or a genus 

 is spread over a larger part of the globe in the course of time, thus 

 becoming mixed with foreign forms. 



After these preliminary remarks, 1 proceed to the special objects of 

 our inquiry ; and we shall then see what conclusions can be formed 

 in comparison with those of the ornithologist*. According to the 

 above-stated peculiarities of the life of Snakes, there is no cosmopo- 

 Utan species, and we can Hnd only a lew examples where one and the 

 aame species extends over the borders of the neighbouring region 

 (cf. p. '378, Naja haje, Echis carinata, Zamenis ventritnacidatua, and 

 p. ;;sj-386, some species ranging from the Nearctic region into the 

 Neotropical, and vice versa). Among the genera we do not find one 

 true cosmopolitan genus. Tropitloaotus is one of those which have the 

 widest range, a genus containing about thirty well-known Bpecies, 

 each of which bears natural characters so conspicuous, that its posi- 

 tion in the system is not to be mistaken : they are not to be found 

 in the .Ethiopian region only; they are truly called freshwater 

 Snakes, following the course of the rivers and the borders ol lakes. 

 Some of the species (T. natrix, hydrut, qutncitneiotus, ordinate*, 

 fasciatus) have a very wide range within the borders of its peculiar 

 region. A few of the Asiatic Bpecies exhibit alighl modifications of 

 the general appearance of the genus ('/'. eeratoffoster and vibakari). 



* As for the systematical denominations adopted, I r< :'. r to tlir ' Catalog 

 Basket' [CroiaUda, Vipcrida, Hydrida . I London, l 



an 1 in my Catalogue of Colubrine Snakes in the I ullceti.ui <>i" 'In Brititb Museum, 

 London, i s ">^. 



