THE DISPERSAL OF SPIDERS 
177
III. THE DISPERSAL OF SPIDERS. 
 In the year that L. Paulus and C. Marcellus were consuls, it rained wool.    
Pliny
. 
For several years L. Berland and I have been in disagreement as to 
the relative importance of the different factors which influence 
distribution. The friendly nature of this contest has been such that 
should either of us in the future be converted to the other's cause there 
would remain, I feel certain, nothing but pleasure for both of us at the 
realization that our joint efforts had ultimately brought us to the same 
conclusions. 
Berland believes that the distribution of species today can be 
explained primarily in terms of (1) former land connections and (2) 
the unwitting transportation of spiders by man in his cargo and ships. 
My views, on the other hand, are (1) that many of the assumed land 
bridges vanished, if they ever existed, too long ago to serve as an 
explanation of the present distribution of species, (2) that man has 
undoubtedly provided the agency by which many species have been 
introduced from one country to another, and (3) that a more important 
factor is the constant interchange of species between neighbouring 
lands by air. 
A. LAND BRIDGES. 
Out of the hundreds of species which have been found embedded in 
Oligocene amber not one, it seems, has survived till the present day, 
so it follows that if importance is to be placed on land bridges these 
bridges must have been in existence at least until Miocene times. In 
point of fact the changes in climate which have occurred since 
Miocene times over a large part of the globe make it 





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