8 ANNALS NEW YORK ACADEMY OF SCIENCES 



transportation may have played a more important part with inverte- 

 brates^ although they cannot be invoked to account for the distribution of 

 vertebrates. The much larger variety and wider distribution on infra- 

 mammalian life in oceanic islands is thus quite to be expected. And the 

 extent and limits of such distribution are in obviously direct accord with 

 the opportunities for over-sea transportation in different groups." 



In the estimate which MatthcAV has made there seems to be an obvious 

 error, for should we postulate 1000 rafts in 300 years we would have 

 10,000,000 rafts during the 3,000,000 years of Cenozoic time, not 30,000,- 

 000 as Matthew has it, and the chances of the whole concatenation of 

 events are reduced by 6Q per cent. But even this reduced estimate would 

 if true bring more mammals to most islands than we find. Let us, how- 

 ever, for the sake of argument, admit that some mammals might be 

 transported in this way, is the premise true that other creatures will be 

 more easily carried? Some will, and these types by their haphazard oc- 

 currence can now be recognized easily; others most certainly will not. 

 Matthew has not realized the enormous sum total of different species 

 which go to make up the fauna of such islands as Cuba and Haiti. Such 

 a vast number of species would require squadrons of rafts at frequent 

 intervals, even if only ancestral stocks were transported from which many 

 species arose after coming to the island by some sort of adaptive radia- 

 tion. Another important point has also been missed. Almost all of these 

 isolated groups of individuals have gro^wn to be well differentiated 

 island species. Distinct from the related forms of the mainland and 

 neighboring islands, they represent t5"pes evolved in complete isolation; 

 an occasional raft bearing individuals from the parent stock would by 

 preventing breeding in, at least in some cases, prevent speciation by isola- 

 tion taking place. 



Let us for a moment consider the Antillean chain as a whole; it is 

 utterly impossible that ocean currents could now or in the past have 

 brought rafts with equal frequency to all parts of this island arc, and yet 

 the same types reappear upon island after island all the way from Cuba 

 to Grenada. Eafting from island to island could certainly not have oc- 

 curred, since there could never have been large rivers on them had they 

 always retained their present size. The fauna is far larger in number of 

 species upon the Greater Antilles than upon the Lesser, as the conditions 

 favorable for the survival of species are obviously better upon the large 

 islands with their luxuriant vegetation than upon such barren islets as, 

 for example, Sombrero or Eedonda. The types, however, which have been 

 able to survive upon Sombrero or Saba are just those which are found, 

 along with many others, upon Cuba or Haiti. In my "Herpetology of 



