NON-AVIAN NEST-MAKERS Mammals.—Few other animals have attained to the skill in weaving displayed by birds. The harvest-mouse among the mam mals is, however, the rival of most birds. The rabbit builds a nest in her burrow, and lines it with the under-fur plucked from her body, forming a parallel to the case of the ducks, geese and swans, which line the nest with down similarly plucked from the breast for this purpose.
The only nest-building mammals which produce eggs are the Echidna, or spiny ant-eater, and the duck-billed platypus or Ornithorhynchus. The nest is of the simplest character, placed in a chamber at the end of a long tunnel dug by the animal.
Reptiles.—Among the reptiles nest-building goes little or no further than digging a hole in the ground, and depositing the eggs within it, leaving them to their fate as in the case of the mega podes among the birds. The European pond-tortoise, however, takes a little more trouble. She first prepares the ground by watering it from the bladder, and from special anal water-sacs. Then, boring a hole with the tail, as one would use a stick, the feet are used to enlarge it. When about five inches deep the eggs are laid at the bottom, and the soil is put back again and beaten down flat.
The crocodile digs a hole in the sand nearly two feet deep, laying her eggs therein and covering them up. But she returns periodi cally to sleep above her treasures. She is thus at hand to assist the young to escape at the time of hatching. She is warned of this by the noise they make in endeavouring to break through the shell; just as young birds announce their advent by cheeping before the shell is actually broken. When they have all emerged the mother escorts them to the water. The alligator, on the other hand, builds a great mound of decaying leaves, mixed with fine earth, to a height of about three feet, and as much as eight feet in diameter. Some eight inches from the surface the eggs, twenty to thirty, white and hard-shelled, are laid.
The python, among the snakes, like Ichthyophis among the Amphibia coils her body around the eggs until they hatch, and guards her young for some time after.
Amphibia.—The Amphibia furnish instances of nidification of a very remarkable character, and at the same time, provide valu able material for the study of behaviour in regard to the parental instincts to serve as a standard of comparison with the higher vertebrates on the one hand, and the lower on the other.
The frogs of the genus Phyllomedusa build nests recalling that of the tailor-bird. The process of this nest-making has been watched in Phyllomedusa hypochondria, the Wollenkukk of the Paraguayan Chaco. The female carries the male upon her back while searching for a suitable leaf—which must be of some tree overhanging the water. This found, both then seize it and hold the
edges together with their hind-feet, while the female pours her eggs into the funnel thus formed, the male fertilizing them as they pass in. The gelatinous envelope of the eggs suffices to hold the leaf-edges in position as they are brought together in the filling process which goes on until about too eggs are laid.
Fishes.—Among the fishes the fresh-water sticklebacks (Gas trosteus) and the marine fifteen-spine stickleback (Spinachia) build nests of weeds, the task being undertaken by the male, who uses, as a binding material, a secretion formed by the kidneys. He undertakes the sole charge of the eggs and young. The gourami (Osphromenus) of the Malay Archipelago fashions a nest of air bubbles toughened by a kind of saliva, and mounts guard over both eggs and young. The Cichlid fishes both of America and the Old World, as well as some of the Siluroid fishes, carry the young in the mouth; in some species both sexes do this, in others the male alone. The male pipe-fish carries the eggs and young in a pouch running along the belly. The Aspredo of the Guianas carries her eggs attached to the under surface of the head, belly and paired-fins. For their accommodation the skin assumes a spongy condition so that each comes to lie within a deep depres sion, recalling the egg-pits of the Surinam toad, but in the case of Aspredo the pits are shallow and the larvae are not retained there.
Invertebrates.—Among the insects the elaborate care for the eggs and young displayed by the ants, bees and wasps is too well known to need further mention. The scorpions and the wolf spiders carry their young about on their backs until they can fend for themselves; and some of the scorpions, again, like the wolf spiders, bear their eggs about closely packed within a spherical silken bag.
Among the Echinoderms we find an Antarctic sea-slug (Cucum aria crocea) carrying the young on its back. One of the sea urchins (Hemiaster philippi), and a starfish (Asterias spirabilis) carry the young in brood-pouches on the back in the case of the sea-urchin, and around the mouth in the starfish. It would seem that only Arctic and Antarctic species behave after this fashion.
In all other cases the young leave the parent as minute, free-swim ming larvae, undergoing a complicated metamorphosis before at taining to the adult form. Here, then, we must regard the care of the young as an entirely impersonal, unconscious act, determined by the physical peculiarities of the external environment. This is a factor to be borne in mind in considering the origin, and evolu tion, of nidification in animals of all grades. (W. P. P.)