EGGS AND EGG-COLLECTING 13 
a wonderful adaptability to the exposed situation chosen 
by this bird for incubation. 
Birds which make round, cup-shaped nests. or incubate 
in holes, such as the Owl and Kingfisher, for instance, 
lay round eggs, which run no risk of rolling away and 
being smashed. Their shape also facilitates alteration of 
position of the parent-bird to secure an equal distribution 
of warmth and ventilation. 
Were the Guillemot and either of the latter birds to 
change nesting situations for a while, it is probable a 
speedy extermination of the species which adopted the flat 
rock for the round egg would soon take place, affording a 
beautiful illustration of the power that is also guiding the 
acticn of birds under the mysterious name of instinct. 
¢ is an unknown and unknowable power, yet its workings 
are as undeniable as its results. 
As a further illustration, let us take the eggs of the 
Golden and Green Plovers, and consider for a2 moment 
their size, shape, number, and colour. 
Ali these qualities serve some well-defined and demons- 
trably useful end. Firstly, their size is abnormally large 
compared with that of the layer, but this is a provision 
which supplies the necessary size and strength of the 
young bird to enable it to cope with the surrounding con- 
ditions of its first days of self-feeding and locomotion 
amongst coarse grass and other obstacles. 
Secondly, the shape of the egg serves to economise space, 
an important point where the eggs are large and the bird 
small. Thus the four pear-shaped eggs, having their small 
ends all pointing to a common centre, practically form a 
square, and thus enable the bird to cover them al! at the 
same time. 
