452 
ISLAND LIFE. 
[rART II. 
the Cretaceous period, the two great forms of birds — those with 
a keeled sternum and fairly-developed wings, and those with a 
convex keel-less sternum and rudimentary wings — already 
existed side by side ; while in the still earlier Archaeopteryx of 
the Jurassic period we have a bird with well-developed wings, 
and therefore probably with a keeled sternum. We are evidently, 
therefore, very far from a knowledge of the earlier stages of 
bird life, and our acquaintance with the various forms that have 
existed is scanty in the extreme ; but we may be sure that birds 
acquired wings, and feathers, and some power of flight, before 
they developed a keeled sternum, since we see that bats with no 
such keel fly very well. Since, therefore, the struthious birds 
all have perfect feathers, and all have rudimentary wings, which 
are anatomically those of true birds, not the rudimentary fore- 
legs of reptiles, and since we know that in many higher groups 
of birds — as the pigeons and the rails — the wings have become 
more or less aborted, and the keel of the sternum greatly 
reduced in size by disuse, it seems probable that the very 
remote ancestors of the rhea, the cassowary, and the apteryx, 
were true flying birds, although not perhaps provided with a 
keeled sternum, or possessing very great powers of flight. But 
in addition to the possible ancestral power of flight, we have 
the undoubted fact that the rhea and the emu both swim 
freely, the former having been seen swimming from island to 
island off the coast of Patagonia. This, taken in connection 
with the wonderful aquatic ostrich of the Cretaceous period 
discovered by Professor Marsh, opens up fresh possibilities of 
migration; while the immense antiquity thus given to the 
group and their universal distribution in past time, renders 
all suggestions of special modes of communication between the 
parts of the globe in which their scattered remnants now 
happen to exist, altogether superfluous and misleading. 
The bearing of this argument on our present subject is, that 
so far as accounting for the presence of wingless birds in New 
Zealand is concerned, we have nothing whatever to do with 
any possible connection, by way of a southern continent or 
antarctic islands, with South America and South Africa, 
because the nearest allies of its moas and kiwis are the 
