viii] MOVEMENT AND MIGRATION 121 



frozen water, while a few earthworms have been 

 brought from the island of Kolguev. These however 

 are quite exceptions to the general sterility as regards 

 earthworms of the excessively cold regions. We have 

 already seen that there are no general facts to be 

 deduced as concerning the relative abundance of 

 terrestrial worms in the tropics and in more temperate 

 climes. Tropical Africa is, it is true, rich in genera 

 and species; but on the other hand tropical East 

 Indies have but few genera inhabiting their numerous 

 islands. Temperate England has very few genera 

 and not a large number of species ; temperate New 

 Zealand has a considerable number of different in- 

 digenous genera. When however we leave this 

 general aspect of the question and consider separate 

 families and genera, there seems to be some little 

 relation between climate and distribution and thus 

 some effect of climate in acting as a barrier to migra- 

 tion. For example, though continuity of land surface 

 permits of the tropical African Eudrilidae ranging 

 southwards as far as the Cape they are not met with 

 so far as we know in the most southern parts of 

 Africa ; nor are the South American Geoscolecidae 

 found in Patagonia or northward beyond Central 

 America. These instances do really look like an 

 influence of climate upon range. On the other hand 

 we must be careful to eliminate the possibility of 

 another explanation and that is the impossibility of 



