vi] PEREGRINE FORMS 107 



temperature is at least one of the causes of a 

 difference in the capability of extending their range 

 shown by the Oligochaeta, a cause which doubtless 

 operates as a check upon extension of range in non- 

 peregrine forms also, and prevents for instance the 

 dispersion of the tropical African Eudrilidae into the 

 region of the Cape. 



We may, as it appears to me, confidently look 

 upon indifference to varying temperature as a con- 

 dition of ability to colonise new countries. But it 

 is obvious that this is not of itself a sufficient cause 

 to explain the facts. Otherwise this country and 

 N. Europe would contain many antarctic earthworms ; 

 the only one that has been recorded to my knowledge 

 is Microscolex. 



Though an inability to endure a temperate climate 

 may have rendered the movements of peregrine 

 species more limited, the same or rather the exactly 

 opposite cause does not seem to have played any 

 important part in this direction. For it is above all 

 the Lumbriciclae, normally dwellers in temperate 

 climates, that are so remarkable for their wide range 

 over the world. Nor can it be convincingly asserted 

 that the extra-Palaearctic Lumbricids are real in- 

 digenes of those often tropical countries. For if so 

 we should expect them to be at least of different species. 

 Lumbricids however from South America, Australia, 

 etc., are specifically identical with European forms. 



