LUTZ, Lh^T OF GREATER ANTILLEAN SPIDERS 133 



times is iudicated, but as it is based on but 2 genera found on the main- 

 land only in Central America and Mexico, 2 found in these regions and 

 South America and 3 found in these regions and United States, it would 

 not be safe to place much reliance on these data. Furthermore such 

 affinit}^ does not demand a land bridge ; it may merely be a result of geo- 

 graphic contiguity and environmental similarity. If Jamaica has always 

 been isolated as it is now, or at least if its last complete submergence was 

 a long time ago and it has since been as isolated as it is now, we can 

 understand the apparent poverty of its fauna, the peculiarity of it and 

 its only slightly stronger affinity with Central America than with the 

 other mainland divisions. 



The impression all these things make on me is that the various An- 

 tilles may always have been as distinct as they are now; that the}^ re- 

 ceived their spider fauna by slow '^accidental" means, and that Porto 

 Eico has only recentl}^ been populated. How, then, are we to explain the 

 ancient character of a large part of its fauna and the curious relation- 

 ships with distant Old World localities? Also, why is the ancient portion 

 of the Cuban fauna more South American than the recent? 



Origin of the Antilleaj^^ Fauna 



Before considering further the origin of West Indian spiders it would 

 be well to note their means of dispersal. Young spiders of nearly, if not 

 quite, all families are more or less given to "ballooning."' They will face 

 against the wind, and, elevating their spinnerets, spin a quantity of fine 

 silk usually in the form of a number of threads. These threads float in 

 the breeze and finally they are numerous enough or long enough to carry 

 their makers on an aerial journey. The length of such journeys would 

 seem to depend very largely on the strength and character of the wind. 

 McCook has attempted to show by its distribution that Heteropoda vena- 

 toria has circumnavigated the globe. It is true that the range of this 

 species corresponds "with remarkable exactitude'' to the belt over which 

 the Trades blow, but we may accept his proof that the species has not 

 been distributed b}^ commerce without adopting his suggestion that its 

 cosmotropical distril)ution is due to its ballooning habit. He cites Dar- 

 win's note about the "Beagle" being boarded by "flying" spiders when 

 sixty miles from land and adds a report which is similar except that the 

 latter ship was more than two hundred miles from land. It must be ad- 

 mitted that wind may be a very efficient factor in the distribution of 

 many organisms, and it should be noted that when spiders go on such 

 journeys they often go in swarms, so that it would not be unlikely that 

 opposite sexes would land near enough each other to continue the species. 



