INTERESTING PROBT.EMS CONCERNING THE AVIFAUNA 357 



As to the periods of semi-starvation, it has to be stated that, 

 among the perching birds, there are in New Zealand four genera 

 of flycatchers — the tits, the wood-robins, the warblers, and the 

 f antails — as well as the wrens, all of which live largely on insects ; 

 and it seems almost certain that these birds must be pushed very 

 hard for a living every winter. There are also nine genera of 

 seed-eaters, or grub-eaters; and these can have no periodical 

 famine time, for the food is abundant all through the year. But 

 none of the insect-eating birds show deteriorated power of flight, 

 while among the others we have the huia, which seldom attempts 

 to fly, the thrush, which cannot rise into the air without making 

 several preliminary hops, as well as the crow, the fern-bird, and 

 the tui, all of ^vhich are feeble fliers. 



There is no reason for supposing that the wood-hens, the 

 kakapo, and the kiwi have any periodical terms of semi- 

 starvation, for all of them are as fat in the winter as in the 

 summer. The parrakeets of the Antipodes Island and the 

 Auckland Islands are as large and as well fed as those of New 

 Zealand, although they have degenerated in the powers of flight. 

 Lastly, as the moas were vegetable feeders, their food in a climate 

 like that of New Zealand must have been independent of the 

 season of the year. Consequently the hypothesis of the necessity 

 for semi-starvation breaks down. Indeed, if a bird was perishing 

 from periods of starvation, wings would be useful to enable it to 

 search more ground, and they would be preserved by natural 

 selection. 



The evidence from New Zealand, therefore, is to the effect that 

 degeneration is not primarily due to natural selection, either in 

 the ordinary way or through a supposed law of compensation of 

 growth. 



The only explanation left is that degeneration is due to 

 disuse-inheritance. 



Disuse we know to be a true cause of degeneration in the 

 individual — it is the only true cause that we know — and everyone 

 will admit that it is the starting point, or originating cause, of 

 degeneration. The difficulty is to explain how variations in an 

 organ, caused by disuse, become progressive. That is, how do 



