124 EARTHWORMS AND THEIR ALLIES [CH. 



explorations of the Ruwenzori chain of mountains 

 in Africa have resulted in the collection of a con- 

 siderable number of species, some of which come 

 from great altitudes {e.g. 4000 metres and slightly 

 upwards), and one species, viz, Dichogaster duwonica, 

 which Dr Cognetti de Martiis described from the 

 foot of the glacier Elena. I have in my temporary 

 possession a number of examples of the eastern genus 

 Pheretima, some of which are new species from lofty 

 areas in the Philippine Islands. There are plenty of 

 other examples pointing to a like conclusion. It is 

 noteworthy that these forms which have been met 

 with at lofty heights are not essentially different 

 from the plain living forms. One cannot exactly 

 speak, at any rate in the present state of our 

 knowledge, of anything like an Alpine fauna. 



It is in fact clear enough that whatever may 

 prove to be the case with regard to particular species, 

 a mountain range is not necessarily a barrier to the 

 dispersal of generic types. 



The Ocean as a Barrier to Migration. 



It is very possible that further investigations into 

 the Oligochaeta will prove that there are more marine 

 forms than those which are enumerated in another 

 chapter. Particularly is this likely to be the case 

 among the family Tubificidae and Naididae. For up 



