HUMMING-BIKDS. 143 



conditions the specific form may then remain unaltered 

 for a very long time ; whence arises the common impres- 

 sion of the fixity of species. Now in a country like 

 Chili, forming part of a great continent very well stocked 

 with all forms of organic life, the majority of the species 

 would be in a state of stable equilibrium ; the most 

 favourable variations would have been long ago selected ; 

 and the numbers of individuals in each species would be 

 tolerably constant, being limited by the numerous other 

 forms whose food and habits were similar, or which in 

 any way impinged upon its sphere of existence. We 

 may, therefore, assume that the Chilian humming-bird 

 which migrated to Juan Fernandez was a stable form, 

 hardly if at all different from the existing species which is 

 termed Eustephanus galeritus. On the island it met with 

 very changed but highly favourable conditions, an abun- 

 dant shrubby vegetation and a tolerably rich flora ; less 

 extremes of climate than on the mainland ; and, most 

 important of all, absolute freedom from the competition 

 of rival species. The flowers and their insect inhabitants 

 were all its own ; there were no snakes or mammalia to 

 plunder its nests ; nothing to prevent the full enjoy- 

 ment of existence. The consequence would be, rapid 

 increase and a large permanent population, which still 

 maintains itself ; for Mr. Moseley, of the Challenger expe- 

 dition, has informed the writer that humming-birds are 

 extraordinarily abundant in Juan Fernandez, every bush 

 or tree having one or two darting about it. Here, then, 

 we have one of the special conditions which have always 

 been held to favour variation a great increase in the 

 number of individuals ; but, as there was no struggle 

 with allied creatures, there was no need for any modifi- 



