CH. I] EARTHWORKS OF SEA SHORE. 57 



The Distribution of Earthworms. 



The geographical distribution of the earthworms offers 

 an instance of a group that is now fairly well known and 

 is at the same time in all probability a moderately ancient 

 group. It has too exceptional qualifications for careful 

 consideration in relation to the theories of past changes of 

 land in connection with the range of existing forms. 

 As a rule earthworms are killed by salt water; there 

 are exceptions such as the genus Pontodrilus which 

 actually lives upon the sea shore within range of at least 

 the splashing of the waves, and it has been asserted that 

 a few species in Ceylon (not named) can withstand the 

 action of sea water. But with these exceptions the ocean, 

 even when in the form of a narrow strait, is an insuperable 

 barrier, which is more effective than any other. As worms 

 have been met with at great heights upon the mountains, 

 there seems to be no particular difficulty in their extend- 

 ing their range by crossing mountain chains; probably 

 also rivers and large lakes are not untraversable ; experi- 

 ments show that earthworms can be kept for some days 

 immersed in fresh water and yet retain their vitality, while 

 there are a good many instances not only of true earth- 

 worms (in structure) which habitually live in the water, 

 but there are species which live with equal ease in water 

 and on dry land. This is true of the European Allurus 

 tetros&rus and of several species of Acanthodrilus. An 

 arid desert would doubtless prove as effectual a barrier to 

 migration as the sea. The only defect in this group with 



