[25]. Where only a small part of the yolk goes to form the fœtus, while the greater part is used to nourish it, as is the case with birds, the egg is called meroblastic. With mammals, all the yolk is used to form the fœtus (holoblastic eggs).
The eggs lying in the ovaries are ⅛ of an inch in diameter, possibly even more, and they certainly are the largest eggs produced by mammals. In a human being and in the higher mammals the egg averages ¹⁄₁₂₅ of an inch in diameter.
The young seem to require a long time to arrive at maturity. They are hatched small, blind, and naked, and their mouths have not at first the form of a beak, but are thick, round, soft, and well adapted to receive the milk, which is strained through the lacteal glands, for there are no nipples. As these animals have no pouch (the ant-eater has a rudimentary one in the form of a crease in the skin while it nurses its young), the young remain in the nest, where the mother suckles them.
Though the ornithology of Australia is not so isolated in its character as the mammals are, still its birds are very remarkable, and have almost as many points of interest. We here find eagles, hawks, thrushes, swallows, fly-catchers, sea-gulls, ducks, etc., though of other species than those to which we are accustomed; but we are astonished that vultures and woodpeckers, which exist in all other parts of the world, are wholly wanting.
The honey-eaters (Meliphagidæ), so well adapted to the circumstances of the country, are very remarkable. As the trees and bushes of Australia have a great wealth of flowers, but are wanting in juicy fruits, many of its birds find their food in the flowers, inhabiting the trees and bushes, particularly gum-trees and banksias, and rarely coming down on the ground to seek food. These characteristic birds, of which there are no less than 200 species, remind us by their mode of life of the American humming-birds; still they are very different from the latter. The largest are of the size of a small dove, but much more slender. They are strong lively birds, which with their powerful feet cling fast to the branches, almost like titmice, while they suck the flowers, and their tongue ends in a brush, so that they can easily lick up the honey and the honey-eating insects. Even some of the parrots, the so-called brush-tongued (Trichoglossidæ), live on honey and pollen, and are peculiar to Australia.
The strange habits of many of the Australian birds have already been described, e.g. the play-houses built by the æsthetic bower-birds, and the three species which do not themselves hatch their eggs, like the reptiles, but leave the hatching to be done by artificial heat. The latter belong to the family of Megapodidæ, a group which receives its name from the fact that their feet and claws are very large and powerful, and consequently well adapted to building the large mounds in which the eggs are laid.
WILD GEESE FROM NORTH QUEENSLAND (Anseranas melanoleuca). Photograph from nature.
It is a strange fact that the kingfishers found everywhere in the world, and the equally cosmopolitan pigeons, should be so numerous in Australia. Among the former are the wonderful laughing jackasses (Dacelo) whose voice is unlike that of any other bird. In Australia the pigeons attain the highest development both as to wealth of species and brilliancy of plumage. Some of them even have a crest on the top of the head, a very rare ornament for this family. The extraordinary development of these defenceless birds indicates that they have but few enemies in Australia. Wallace gives as the reason for their great numbers the total absence of apes, cats, weasels, and other animals that live in trees and that eat the eggs and the young of birds, while the very green colour of these birds conceals them from birds of prey, their only foes. On the plains in the interior of Queensland countless numbers of pigeons are seen, but of modest-coloured plumage, to protect them in this open country.
Many of the Australian birds are distinguished for their brilliant plumage, and in this respect they easily rank with the humming-birds of America and with the trogons and parrots of India. Thus we have the elegant little wrens whose leading colours are azure blue and scarlet-red; the yellow and velvety black regent-bird (Sericulus melinus); and the metallic glittering rifle-bird (Ptilorhis victoriæ); and finally, the finches, that have a combination of colours the like of which is to be found only in butterflies. Among the many parrots, which include such strange forms as the white and the black cockatoos, there are some which are unique in the beauty of their colours. So remarkable a decoration as the tail of the lyre-bird (Menura) is found nowhere else in the world of birds.