108 THE VARIATION OF ANIMALS IN NATURE 



in spite of their powers of flight, bats are as much prone to 

 form subspecies as other mammals. Possibly this is explicable 

 on the grounds of localised range, though no facts can be 

 produced to support this suggestion. Among reptiles the 

 common African tortoise, Testudo pardalis, ' extends practically 

 over the whole continent . . . and is everywhere uniform 

 as regards its colour-pattern ' (Duerden, 1907, p. 74). 



Land molluscs tend to fall into well-marked local races 

 in spite of Rensch's statement. These are especially well 

 marked if the terrain is favourable to isolation (Gulick, 

 Crampton, Bartsch, Mayer, Sarasin, Simpson). Even when 

 these conditions are absent, races may be formed as in Murella, 

 Helicogena and Iberus (Kobelt), Otala (Boettger), and in sundry 

 African species (Pilsbry). On the other hand, certain forms 

 such as Carychium (Thorson and Tuxen, 1930) show no such 

 tendency. Again, in such forms as Cepea and Cochlicella, though 

 statistical differences occur in the percentage incidence of 

 colour-patterns in various colonies, there is no regional differ- 

 entiation worth mentioning. In contrast with the acute 

 local polymorphism of Achatinella and Partula in the valleys of 

 the Sandwich and Society Islands, the land snails of the valleys 

 of Valais (Piaget, 1921) show no such variation, and although 

 numerous insular races are found in Liguus on the Florida 

 Keys (Simpson, 1929), Ampkidromus in the Philippine Islands 

 (Bartsch), etc., the land snails of the Hebrides and Scilly Isles 

 are, as far as they are known, quite like the mainland forms. 



Amongst insects, taxonomy is still, as a rule, insufficiently 

 advanced to allow certain conclusions to be drawn. It is 

 probably significant, however, that in the minute, wingless 

 Collembola the species often have a very wide range without 

 any apparent signs of local differentiation. Uvarov (1924) 

 records an interesting example in the grasshoppers of the 

 genus Cyrtacanthacris. C. tatarica is found over the whole of 

 South and Equatorial Africa, including Madagascar, Seychelles, 

 Comoro Is., Khartum, Massourah, Sokotra, India, Siam and 

 Ceylon. There is no geographical variation and the species 

 is extremely constant, though very common. On the other 

 hand, C. aeruginosa, which is purely African, has three races, 

 a southern, a western and an eastern race. 



It is a remarkable fact (and one which might seem to be 

 easily explicable on the grounds that there are no barriers 



