NOVEMBER 275 



or, at least, complying with the habit, which has 

 become binding upon its kind. Its acquaintance with 

 the obligation may be considered functionally instinc- 

 tive; but it involves a performance of unusual com- 

 plexity. Compliance with an established custom is 

 comparatively easy to understand ; at all events, it may 

 appear to be so ; but speculation goes adrift in attempt- 

 ing to explain how the custom became established. 

 No matter how big the feet and powerful the shanks 

 of the primeval megapode may have been no matter 

 how much unconscious satisfaction it may have derived 

 from exercising these organs in piling mounds how 

 did it hit upon the labour-saving secret that ferment- 

 ing vegetable substance would supply heat enough to 

 bring the eggs to the hatching ? Ordinary evolutional 

 analogy seems to provide no key to fit these compli- 

 cated wards, neither is one tempted to credit the fowl 

 with knowledge that fermentation generates heat. It 

 is possible that, seeing how prone all gallinaceous fowls 

 are to scraping, the original megapodes may have so 

 excelled in that activity as to have thrown together a 

 fortuitous heap of rubbish, which generated a per- 

 ceptible heat, thereby tempting them to deposit therein 

 their eggs. It is well known that mother birds of 

 all species never leave the nest during the period 

 of incubation for so long a period as shall expose the 

 eggs to chill. Their absence, in our climate at least, is 

 always exceedingly brief. So the megapode may have 

 found by experience that she could safely leave her 

 eggs in the rubbish mound for a much longer period 

 than in an ordinary nest; until at last, finding the 



