354 THE ANIMALS OP NEW ZEALAND 



AVe can understand how natural selection may have strengthened 

 the bill in the thrush and elongated it in the huia, as we can see 

 that both are useful; but we cannot see that the differences just 

 mentioned are useful to the birds. Most of these cases are 

 evidently connected in some way with isolation ; but there are 

 exceptions, as in the fern-bird, the fantails, the wood-hens, and 

 the kiwis. 



The case of the wood-hens is especially interesting. Here we 

 find the North Island wood-hen in Stewart Island, but not in the 

 South Island. In the South Island there are four other species, 

 each of which is fairly well confined to its own district. The 

 South Island wood-hen inliabits the low lands all round the 

 islands ; the hill wood-hen is found on the hills, the black wood-hen 

 in the West Coast Sounds, and Finsch's wood-hen in the neigh- 

 bourhood of Lake Te Anau. The South Island wood-hen is also 

 found in Stewart Island, where it seems to interbreed 'with the 

 North Island wood-hen, if we may judge from the number of 

 individuals that come from there which are intermediate in 

 plumage between the two. Although hybrids are very rare in 

 a natural state, it is possible that Finsch's wood-hen may be a 

 hybrid between the black wood-hens and the ^outh Island wood- 

 hens. 



The only explanation of these facts seems to be the supposition 

 that at one time the North Island wood-hen spread over all three 

 islands, and that it remained unaltered in the North Island, while 

 in the South it gave rise to the South Island and black wood-hens 

 and then disappeared, the hill wood-hen being afterwards derived 

 from the South Island Avood-hen. But it is hard to say why these 

 differences should have arisen. 



Another very interesting case is that of the yellowish parrakeet, 

 which has been found at the Antipodes Island and Macquarie 

 Island. It differs from the red-fronted pan-akeet by its yellow 

 tint. It is extremely improbable that the parrakeet of IMacquarie 

 Island came from Antipodes, or vice versa. The islands are 

 further apart than either of them is from New Zealand; and 

 both Auckland and Campbell Islands, on which the species is not 

 found, lie close to the track. The j'ellow tint is due to a failure of 



