VII] EARTHWORMS OF OCEANIC ISLANDS 109 



not so evident ; and the strong rays of the sun 

 appear to drive them further underground and into 

 marshes; this obviously lessens the chance of their 

 accidental transference by man. Furthermore 

 Dr Eisen has pointed out that the European species 

 are apt to have clitella and to be fertile all the 

 year round, which is not always the case wdth other 

 genera. That naturalist has added to this observation 

 the fact that in rich cultivated soils in California it is 

 impossible to find anything but imported European 

 species, since cultivation itself appears actually to 

 drive away the native forms. 



CHAPTER VII 



THE EARTHWORMS OF OCEANIC ISLANDS 



Oceanic islands are islands that have always been 

 islands, a definition that seems tautological until we 

 compare it with some other land masses that may be 

 termed * islands.' Geology teaches us in fact that from 

 the point of view of their origin islands may be 

 divided into two quite sharply contrasted classes. 

 There are those detached land masses usually lying 

 near to or comparatively near to some continent, 

 which have been in the course of time detached by 

 the action of the waves from that continent, such 



