206 NEW ZEALAND NATURE-STUDY BOOK 
Time of mating—kind of nest—where built—time 
taken in building — number of eggs — time 
taken to hatch—whether hatching done by one 
or both birds—time taken for young to grow 
up and leave nest—food of young, ete., ete. 
XVI.—A BIRD'S EGG. 
INTRODUCTION. —A bird’s egg consists of a hard covering or 
shell inside of which are the white and the yolk—the former being 
colourless, and the latter yellow and opaque. As soon as the eggs 
are laid, the mother keeps them warm by sitting on them for some 
time. The effect of this being that the contents of the egg 
gradually develop into a young bird. 
Shape and what it teaches. It is needless to say 
that much variety of shape is found amongst eggs. In 
some cases the eggs are spherical, in others almost cone- 
shaped whilst between these extremes nearly every inter- 
mediate form is found. The surface of the egg is every- 
where curved, in other words the egg is always more or less: 
round, a shape which has quite a number of advantages to: 
recommend it. 
(1) It is the most comfortable to sit upon—in no other 
shape could angular projections—more or less sharp—be 
avoided. 
(2) Itis the shape which gives the greatest strength to: 
the shell—an important matter when we bear in mind the 
weight of the sitting bird. 
(3) It is the shape which enables the bird most easily 
and safely to turn her eggs in the nest. The reasons for 
this operation will be discussed in the next chapter. It is 
carried out by means of the feet and beak of the bird, and, 
