vi] PEREGRINE FORMS 103 



able to establish themselves in Europe. Dr Michael- 

 sen also relates that in the cultivated lands of South 

 West Australia, Microscolex clublus and Helodrilus 

 caliginosus are actually the commonest species ; and 

 he calculates that they form together quite 90 % f 

 the earthworms gathered in any locality belonging to 

 this region. 



Some of the other Megascolecid peregrine forms 

 will be referred to later. There is no doubt that the 

 family Lumbricidae offers by far the greatest number 

 of peregrine forms and that these are most abundant 

 in collections from extra-European countries, where 

 the collector has searched in cultivated lands. There 

 are at least eight or nine species which are common 

 in many parts of the world though their original home 

 is undoubtedly Europe. 



This is a brief review of the facts, more detailed 

 in some cases than in others. It remains to review 

 and compare the results arrived at. 



The first general statement that may be made is 

 that this faculty of extending their range beyond the 

 limits assigned by nature is not confined to any one 

 family. For all the chief sub-divisions of the terres- 

 trial Oligochaeta seem to possess it, though in unequal 

 degrees. But the inequality may be more apparent 

 than real. For if it be recollected that the species 

 of the family Megascolecidae are very much more 

 numerous than those of the Eudrilidae or even the 



