Cormorants 



totally in the dark as to what causes them. 

 They arise at the most unexpected times. 



In favour of the explanation based on " muta- 

 tion " there is the interesting fact that geographi- 

 cal isolation does not by any means always cause 

 divergence of character. This Romanes, with 

 great fairness, freely admits. " There are/' he 

 writes, on p. 133 of vol. iii. of Darwin and 

 after Darwin, " four species of butterflies, belong- 

 ing to three genera (Lyccena donzelii, L.pheretes, 

 Argynnis pales, Erebia manto\ which are iden- 

 tical in the polar regions and the Alps, notwith- 

 standing that the sparse Alpine populations have 

 been presumably separated from their parent 

 stocks since the glacial period." Again, there 

 are "certain species of fresh- water crustaceans 

 (Apus), the representatives of which are com- 

 pelled habitually to form small isolated colonies 

 in widely separated ponds, and nevertheless 

 exhibit no divergence of character, although 

 apogamy has probably lasted for centuries." 



To these examples we may add that of the 

 cormorants. These birds have an almost world- 

 wide range. One species our Cormorant 

 (Pkalacrocorax carbo] occurs in every imagin- 

 able kind of environment. Isolation has not 

 effected any changes in the appearance of this 

 species. Yet in New Zealand there exist no 

 fewer than fourteen other species of cormorant. 

 New Zealand is a country where climatic con- 



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