THE EGGS OF BIRDS. 627 



Usually the hen does most of the work, but her mate sometimes helps, 

 both in building the nest and in hatching the young. 



The nest is a cradle rather than a house, for its chief use is to secure 

 an approximately constant warmth for the young which are being 

 formed within the eggs, and to afford protection for the helpless 

 fledglings. At the same time, the nest secures the comfort of the 

 parent bird during the days and nights of brooding. 



The variety of nests may be illustrated by mentioning the burrowed 

 nests of sand-martins and kingfishers, the ground-nests of game-birds 

 and gulls, the mud-nests of house-swallow and flamingo, the holes 

 which the woodpecker fashions in the tree stem, the platforms built by 

 doves and eagles, storks and cranes, the basket-nests of most singing- 

 birds, the structures delicately woven by the goldfinch, bullfinch, and 

 humming-birds, the sewed nest of the tailor-bird, the mossy nests of the 

 wrens, the edible nest of the Collocalia, which is chiefly composed of 

 mucin secreted by the salivary glands. 



The Eggs of Birds. — When the nest is finished, the eggs are ready to 

 be laid. After they are laid, the patience of brooding begins. With 

 the great care that Birds take of their young we may associate the 

 comparatively small number of the eggs ; but it is more accurate to 

 recognise that, as animals become more highly evolved, the number of 

 offspring decreases. Yet it must be remembered that inductions of this 

 kind are only generally true, for subsidiary conditions often bring about 

 the apparent contradiction of a general truth. Thus we are not justified 

 in saying that the Apteryx, which lays one egg, is a more highly differen- 

 tiated bird than the ostrich, which lays many. 



The size of the egg usually bears some relation to the size of the bird. 

 Of European birds, the swans have the largest eggs, the golden-crested 

 wren the smallest. It is said that the egg of the extinct A/oa sometimes 

 measured nine inches in breadth and twelve inches in length ; while 

 that of the extinct .^'Epyornis held over two gallons, some six times as 

 much as an an ostrich's egg, or a hundred and fifty times as much as 

 a fowl's. Yet the size of the egg is only generally proportional to that 

 of the bird ; for while the cuckoo is much larger than the lark, the eggs 

 of the two are about the same size ; and while the guillemot and the 

 raven are almost of equal size, the eggs of the former are in volume 

 about ten times larger than those of the latter. The eggs of birds, 

 whose young are rapidly hatched and soon leave the nest are large. 

 Professor Newton remarks that " the numl^er of eggs to be covered at 

 one time seems also to have some relation to their size," while from what 

 one notices in the poultry yard, and from a comparison of the habits of 

 different birds, it seems probable that a highly nutritive, sluggish bird, 

 will have larger eggs than a bird of more active habit and sparser diet. 



The shell of the egg is often very beautifully coloured ; there is a 

 predominant tint upon which are spots, streaks, and blotches of varied 

 colour and disposition, so that the egg is almost always characteristic of 

 the species. The colouring matter con.sists of pigments related to those 

 of the blood and the bile, and is deposited while the shell is being 

 formed in the lower part of the oviduct. As the eggs may move before 

 the pigments are fixed, blotchings and markings naturally result. But 

 the most interesting fact in regard to the colouring of the egg shells, is 



