viii] MOVEMENT AND MIGRATION 113 



CHAPTER VIII 



MOVEMENT AND MIGRATION AMONG EARTHWORMS 



That earthworms can move upon the surface of 

 the ground at a rapid pace is probably well enough 

 known to everyone, and that they can also burrow 

 with considerable celerity. Multiplying the inches of 

 progress in minutes of time by centuries with the 

 resulting miles, it is quite clear that there is no 

 reason to suppose that an individual earthworm 

 might not enormously extend its range under favour- 

 able circumstances. Their powers of locomotion are 

 such that they could in the course of comparatively 

 few centuries people a continent. As a matter of 

 fact these animals are frequently very widely spread 

 upon a given land surface; but on the other hand 

 they are sometimes equally limited. It behoves us 

 therefore to enquire the reasons for the possibility of 

 extended migration and the causes which have led to 

 its restriction. We are now, it must be borne in mind, 

 considering these animals as purely terrestrial animals 

 moving over the surface of the land by their own 

 unaided efforts. We leave out of consideration any 

 possible assistance in crossing water, whether fresh 

 or salt. We have to consider in fact in the present 



B. E. 8 



