248 THE DISTRIBUTION AND CIIARACTKRS OF REPTILES. 



habit should accompany structural divergences, intermediates are 

 less likely to persist. 



Are specific characters adaptative? — A great many instances 

 of utility in trivial characters have been brought together by 

 Darwin, Wallace, and their followers, but the structural charac- 

 ters which separate species are not usually regarded by system- 

 atists as of particular value to their possessors. For example, 

 two allied species of antelope, T.ichtenstein's Hartebeest and 

 the Red Hartebeest, are distinguished by the form of their horns. 

 Now whilst admitting the general utility of horns in antelopes, it 

 is hard to 'believe that the particular form of horn in either 

 species lis specially adapted to the peculiar needs of that species. 

 But one may argue, as the Darwinists do. that our ignorance of 

 the minutiae of the life history of species is so profound that we 

 can form no proper conception of the function of such charac- 

 ters : moreover, it is possible that structures which at one time 

 were of great importance have now ceased to be of use. This 

 latter argument can only be applied with great caution, but it 

 should not be overlooked. The extraordinary protective devices 

 which are such a feature of the Karroo insect fauna and the 

 remarkable facts of mimicry amongst our butterflies must in 

 terms of the simplest theory which can explain those facts imply 

 a high degree of usefulness in the characters concerned, either 

 to-day or in past times ; yet in the case of the butterfly miinics 

 at any rate, the necessary facts required to prove the utility of 

 the deception — r/rr., the decimation of unprotected butterflies in 

 enormous quantities by discriminating foes, and the immunity of 

 mimics and mimicked species — seem to be almost entirely lacking, 

 and we have to assume that the mimicry was evolved at a time 

 when the struggle for existence amongst butterflies was much 

 keener that it is to-day. Again, as is well known, orchid flowers 

 are constructed with some elaborate mechanisms for bringing 

 about cross-fertilisation through the agency of insects, and the 

 majority of species cannot be self fertilised; but quite a numlber 

 of species are known in which the same beautiful contrivances 

 are still found, and yet the species are no longer dependent on 

 insects, being always self-fertilising. 



Amongst re])tiles the structural characters which separate 

 species onlv rarely appear to be undoubtedly useful. Examples 

 are found in Typhlosaurus lineatus or Typhlops schiiiri. which 

 are both separated from their allies by the possession of a sharp 

 cutting snout, enabling them to burrow in the sun-baked soil of 

 the Kalahari. The window-eyelids of several species of the 

 genus Rronias may also be counted in this category. 



In the frogs, adaptative differences often separate the main 

 groups of species in a genus: for instance the aquatic species of 

 Rana have broadly-webbed feet, whilst grass frogs have only 

 slightly weblbed feet. But when we consider the differences 

 between the most closely allied species, rather than between the 



