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 (Lycena donzelit, L. pheretes, 
Argynnis pales, Evrebia 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 
(Agus), 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 
(Phalacrocorax 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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