GENERAL CHARACTERISTICS. 301 



As already mentioned, birds produce their young- by means of 

 s ' eo-o-s 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 Eorm, mainly pertain to the wading- 

 birds and their terrestrial allies the plovers, of the order Limicolae; 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 tin- nest, witli 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 

 Hedged. 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 laving 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 lie 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. 



