6 EGGS AND EGG-COLLECTING. 
Instinct is an extremely difficult power to define, and 
whether it be described as “ hereditary habit,” or simply 
accepted as an unknown law of Nature blindly followed 
by its possessor, it cannot be denied that it is the outcome 
of conditions, and always amenable to them. If the word 
mystery were often substituted for instinct, it would not 
be at all out of place, for it means quite as much. It is 
more honest to acknowledge our ignorance than to fence it 
round by speculative theory or cover it by almost mean- 
ingless phrases. Survival of the fittest is undoubtedly 
Nature’s great law. With this end in view she governs 
and regulates the actions of birds in exactly the same way 
as she controls the colour and character of their plumage, 
shape, size, tint, and number of their eggs, first move- 
ments of their young, and other peculiarities we do not 
understand. 
If we grant that birds possess highly-developed imita- 
tive faculties and tenacious memories, with a discriminating 
power which enables them to adapt certain habits of life 
to surrounding conditions, even this fails to explain a 
great deal. Supposing it is the secret of their beautiful 
nest-building, the house sparrow adopting trees to nest in 
where the houses are built of brick and lack crevices, or 
the falcon deserting its usual high inaccessible crag and 
nesting on the ground; it cannot possibly account for a 
young duck taking the water directly it has left the shell, 
or the habit of young plovers, snipes, grouse, and other 
birds crouching flat when danger is overhead even as soon 
as they are hatched. A stronger point still is migration, 
for birds cannot return to their old haunts by a memory 
of landmarks, as pigeons do even in their longest flights, 
for they fly over immense bodies of water and traverse 
