GENERAL CHARACTERISTICS 1473 



are enabled to conceal themselves among water plants, and can thus protect them- 

 selves without flight, the shedding of all the wing feathers is frequently almost 

 simultaneous. 



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 Limicoltz; 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 amout of space. Sea birds like the guillemot and razor- 

 bill, 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. More- 

 over, 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 porcelaneous 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 emu 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 

 color 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 colored by 

 the deposition of pigment on or near the outer surface of the shell. The color (as in 

 the tinamus) may be either uniform over the whole surface, or it may take the form 

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