ANIMAL INTELLIGENCE. 21 
innate proclivity, which, like other idiosyncrasies, attains its 
highest activity at the season of reproduction. When the 
adult Megapode combines for the first time with others of its 
species to construct and stock the incubating mound it is 
obeying the law, or at least complying with the habit, which 
has become binding upon its kind. Its acquaintance with 
the obligation may be considered functionally instinctive ; 
but it involves a performance of unusual complexity. Com- 
pliance with an established custom is comparatively easy to 
understand—at all events, it may appear to be so—but specu- 
lation goes adrift in attempting to explain how the custom 
became established. No matter how big the feet and power- 
ful 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 fermenting 
vegetable substance would supply heat enough to bring the 
eggs to the hatching? Ordinary evolutional analogy seems 
to provide no key to fit these complicated wards, neither is 
one tempted to credit the fowl with knowledge that fermen- 
tation generates heat. It is possible that, seeing how prone 
all gallinaceous fowls are to scraping, the original Mega- 
podes may have so excelled in that activity as to have thrown 
together a fortuitous heap of rubbish, which generated a 
perceptible heat, thereby tempting them to deposit therein 
their eggs. It is well known that mother birds of most 
genera 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 irksome duty of personal incubation to be superfluous, 
she abandoned the practice. 
It will be observed that this hypothesis assigns to the 
mother Megapode a high degree of intelligent observation 
and sagacious application of experience. It may be com- 
pared with the discovery made long since by human mothers 
that the substitution of the bottle for the breast in rearing 
