122 EARTHWORMS AND THEIR ALLIES [ch. 



successful migration owing to the previous occupa- 

 tion of the ground with abundant other forms. The 

 very same countries would appear to show that this 

 explanation is unnecessary. For the prevalent genus 

 of the southern tracts of South America Notiodrilus 

 extends its way northward as does the same genus 

 from temperate to tropical Africa and Madagascar. 



It looks very much, therefore, as if certain Oligo- 

 chaeta are dependent upon climate for their range, 

 and as if others were at least more independent of 

 climatic conditions. And there are other facts which 

 support this view. The same opinion is supported 

 by the phenomena of involuntary migration, a subject 

 which has been considered also separately under the 

 head of ' Peregrine forms.' The great prevalence of 

 Lumbricidae accidentally imported into many parts of 

 the world shows that temperature is no real bar to 

 their voluntary migration. On the other hand the fact 

 that specimens of the East Indian genus Pheretima 

 though commonly imported accidentally into the 

 warmer regions of the world have not been able to 

 make good a footing in Europe, save in greenhouses, 

 shows that this genus is atiected in its range by 

 questions of climate. These facts suggest another 

 inference of great interest which can only be 

 mentioned tentatively, and not put forward as a 

 demonstrated conclusion. Seeing that Lumbricus 

 {sensu lato) can comfortably take up its home in 



