236 BARBOUR: ZOOGEOGRAPHY. 



The introduction of tiie mongoose has, in Grenada as elsewhere, resulted 

 in marked changes affecting the relative abundance of many animals, and none 

 have suffered more than the reptiles. In writing of several species, I have in- 

 cluded notes furnished me by Dr. Allen regarding mongoose ravages. I have 

 previously had something to say regarding the conditions in Jamaica, and there 

 as in Grenada, the same genera seem to have suffered most from the introduction 

 of this pest (Barbour, Bull. M. C. Z., 1910, 52, p. 270-301). 



CONCLUSIONS. 



The fauna of the West Indian region as a whole is homogeneous ; that is to 

 say, certain genera, as for instance .Ameiva, probably derived from northeastern 

 South .America, have penetrated through the chain with a local species upon 

 practically every island, and reached as far as Cuba and Jamaica. Naturally, 

 the types derived from South America are most abundant in the islands which 

 were last in connection with South America, as in Grenada; and disappear 

 gradually, dropping out one by one, until but comparatively few reach the 

 Greater Antilles. Conversely, types of Central American origin predominate 

 in Cuba and Jamaica; Central American types, derived through both of these 

 islands, occur on Haiti and Porto Rico. Other genera which may be called 

 purely Antillean are found throughout the entire group of islands ; and the most 

 characteristic of these are Alsophis and Leimadophis, whose distributions parallel 

 one another in a most remarkable manner, as does also the distribution of Eleu- 

 therodactylus. There is no use in expanding upon the hmits of extent of the 

 other genera, as these may easily be seen by referring to the tables. The point, 

 however, which is most worthy of emphasis is that this homogeneous fauna is 

 characteristic not only of reptiles and amphibians, but of birds and mammals, 

 as well as of groups of terrestrial invertebrates, Peripatus affording an excellent 

 example. When this fact is taken into consideration with the regularity with 

 which the important genera occur on practically every island that has been scien- 

 tifically explored, with a species pecuhar to each, it becomes evident at once that 

 these groups of individuals on each island have been isolated for a long time, and 

 that evolution by isolation would be impossible if individuals were being carried 

 from one island to another by flotsam and jetsam dispersal. The inherent 

 tendency of any isolated group of individuals to vary in some definite direction 

 and to fix peculiar characters within the group would be impossible if a constant 



