90 EARTHWORMS AND THEIR ALLIES [oh. 



obvious. It may also be extended if we confine 

 ourselves to species and not to genera. For the two 

 great islands of New Zealand have not between them 

 more than fifty species of earthworms, while Australia 

 has four or five times that number. It will be noticed 

 however that we cannot associate poverty of generic 

 differentiation with limited land masses; for New 

 Zealand has a large number of generic types, very 

 many more than the huge Euro-Asiatic tract of 

 continent. 



The Range of Genera. 



We have seen, and shall again refer to the fact, 

 that individual species of earthworms have not as 

 a rule a range over a great extent of country, save 

 only in those cases such as Pheretima hetei'ochaeta 

 which belong to that physiological section of these 

 worms called 'peregrine' forms; these appear to 

 possess some means of extending their range by the 

 assistance of man which is denied to other forms. 

 Apart from these instances, which do not come under 

 the present category, it is only Lunihriciis and its 

 immediate allies, Helodrilus, etc., of which certain 

 species are found to exist over wide tracts of land. 

 There are however many genera which have a wide 

 range and which may be contrasted with others in 

 which the range is very limited. The two extremes 



