122 BIRD LIFE ON ISLAND AND SHORE 
passed over because internal. There is in fact a 
constant tendency amongst septs of a species, 
under varying circumstances of food and climate, 
towards small dissimilarities in colour, size, song, 
and, I believe, too, in shyness of disposition. 
We have but to suppose the discovery of New 
Zealand postponed by a few thousand centuries, 
to imagine the arrival of ornithologists who note 
the fact that Bellbirds breed in holes; the trans- 
formation effected, the link gone, the process of 
change complete, the fact alone would remain. 
Should such an alteration yet take place, a hint 
at any rate will now have been registered as to the 
why and wherefore. 
Another of these departures from typical habits 
—departures sure sooner or later to induce struc- 
tural variation—seems to be displayed in the Bush 
Wren. Watching its way of life, many interest- 
ing speculations passed through my mind as to 
the result of the crowding of species on to yet 
unsubmerged portions of a sunken land mass. In 
the movements of this tiny bird, once more it 
seemed that I might be watching steps—adum- 
brations, at any rate—towards the creation of a 
new species. In the case of the Bush Wren it is 
indeed almost possible to show the positive, com- 
parative, and superlative of change. We must 
first picture the bird as described in times prior 
to the rat and weasel plague. It was then com- 
