GENERAL GEAR A Cl ERISTICS. 
301 
As already mentioned, birds produce their young by means of 
eggs, covered with a hard calcareous shell, often remarkable for the 
beauty of its coloration. Into the structure of an egg it will be quite unnecessary 
to enter in this work; but the following remarks, chiefly taken from the 
descriptive account of a series of some of the most remarkable forms in the 
central hall of the British Museum, will be found of general interest. Although 
the number of eggs laid and incubated together is generally pretty constant in 
each kind of bird, yet there is great specific variation in this respect. The Manx 
shearwater, for instance, lays but a single egg, while clutches of the long-tailed 
tit and red-legged partridge may contain from nine to twelve eggs. In form, eggs 
vary from an almost spherical shape, as in owls, to different modifications of the 
elliptical or oval. The latter shape, in which one end is smaller and more pointed 
than the other, although far from being universal, is decidedly the most common; 
this conical shape allowing a larger number of eggs to be accommodated in a 
circular nest than would otherwise be possible ; and it may be noticed that, when 
only a pair of eggs is laid, this form is but seldom assumed. Such eggs as narrow 
very rapidly, and thus take a pear-shaped form, mainly pertain to the wading- 
birds and their terrestrial allies the plovers, of the order Li mi coke; four of these 
being laid in a nest. Their size being large in proportion to the bulk of the bird 
by whom they are laid, their position in the nest, with their pointed ends meeting 
together in the centre, causes them to occupy the smallest possible amount of space. 
Sea-birds, like the guillemot and razorbill, which lay one or two eggs on barren 
ledges of rock, likewise have them pointed, as being much less liable to roll than 
would be the case if they were spherical. 
Although the size of the eggs generally varies proportionately to that of the 
parent bird, yet this is by no means invariably the case; and it appears that 
in birds of which the young are hatched in a helpless condition, the eggs are 
relatively smaller than in those in which the young come into the world fully 
fledged. Moreover, it is the birds that have helpless offspring that usually 
make the most carefully constructed nests; while those that have fully fledged 
young lay their eggs in very rude nests or on the bare ground. As examples of 
birds of equal size, laying differently sized eggs, may be mentioned the curlew and 
the raven; while the bird which has the relatively smallest egg is the cuckoo, 
and that with the largest the kiwi. 
The texture of the outer surface of the shell is liable to much variation, 
tinamus and kingfishers laying smooth and porcellaneous eggs, while those of the 
ibises and ducks are dull and chalky, those of the flamingos coated with a 
calcareous outer film, and those of the emeu rough and pitted. As regards 
coloration, no relation can be traced between eggs and the birds by which they are 
laid; and it is probable that originally Birds resembled Reptiles in laying white 
eggs, this want of colour being retained, or perhaps reacquired, in the eggs of the 
majority of birds which lay in holes. The larger number of eggs are, however, 
variously coloured by the deposition of pigment on or near the outer surface of 
the shell. The colour (as in the tinamus) may be either uniform over the whole 
surface, or it may take the form of irregular washes, blotches, lines, or more or 
less nearly circular spots, upon either a white or uniformly-coloured ground. 
