OVERLAND TO LA ESPERANZA 23 



nent" has been broken into several long series of 

 interrupted sierras and the innumerable "islands" 

 mogotes. The constant mutations slowly going 

 on in all living species are most strikingly shown by 

 a comparative study of the life, especially of the 

 mollusks, that have suffered isolation upon the 

 lesser sierras and the mogotes; indeed the answer 

 to most of the puzzles concerning the origin and 

 the development of the Cuban fauna must be 

 sought in the modified faunas of the mogotes. This 

 line of investigation, with abundant material 

 offered for study, becomes a most absorbing one. 



In every faunal area of the world there are 

 certain genera that appear to be more "plastic" or 

 quick to adapt themselves to changing conditions 

 of life. Among land snails the Cerions of the 

 Bahamas and coastal Cuba, the Clausilias of 

 Europe and Asia, and the Urocoptids of the 

 Antilles may be cited as good examples. Many 

 more could be given of quite the opposite charac- 

 teristics among genera and species which have 

 suffered extermination through comparatively 

 slight changes of environment. Hence for material 

 for evolutionary study we were always hunting for 

 mogotes in Cuba and on the mogotes our special 



