THE EGGS OF BIRDS. 497 



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 wood- 

 pecker 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 the 

 secretion of 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 num- 

 ber 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 in- 

 ductions 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 Moa sometimes measured nine inches 

 in breadth and twelve inches in length : while that of the 

 extinct .Mpyornis held over two gallons, some six times as 

 much as 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 have 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. Hewitson 

 has noted that the eggs of birds, whose young are rapidly 

 hatched and soon leave the nest, are large ; Professor 

 Newton remarks that " the number of eggs to be covered at 



