Page:Encyclopædia Britannica, Ninth Edition, v. 19.djvu/224

Rh 214 PLATYPUS also will be found the main distinctive characters of the two existing representatives of the group. It is there stated that the early stages of the development of the young are not yet fully known ; in fact this was till very recently one of the most interesting problems in zoology to be solved. It has been repeatedly affirmed, in some cases by persons who have had actual opportunities of observa tion, that the platypus lays eggs; but these statements have been generally received with scepticism and even denial. This much-vexed question has, however, been settled by the researches of Mr W. H. Caldwell (1884), who has found that these animals, although undoubtedly mammals throughout the greater part of their structure, are ovipar ous, laying eggs, which in the manner of their development bear a close resemblance to the development of those of the Reptilia. Two eggs are produced at a time, each measuring about three-fourths of an inch in its long and half an inch in its short axis, and enclosed in a strong, flexible, white shell. The platypus is pretty generally distributed in situa tions suitable to its aquatic habits throughout the island of Tasmania and the southern and eastern portions of Australia. Slight variations in the colouring and size of different individuals have given rise to the idea that more Platypus. Fr juld s Mammals of Australia. than one species may exist ; but all naturalists who have had the opportunity of investigating this question by the aid of a good series of specimens have come to the con clusion that there is but one ; and no traces of any extinct allied forms have yet been discovered. The length of the animal when full grown is from 18 to 20 inches from the extremity of the beak to the end of the tail, the male being slightly larger than the female. The fur is short, dense, and rather soft to the touch, and composed of an extremely fine and close under-fur, and of longer hairs which project beyond this, each of which la very slender at the base, and expanded, flattened, and glossy towards the free end. The general colour is deep brown, but paler on the under parts. The tail is short, broad, and depressed, and covered with coarse hairs, which in old animals generally become worn off from the under surface. The eyes are small and brown. There is no pro jecting pinna or ear-conch. The mouth, as is well known, bears a striking resemblance to the bill of a duck. It is covered with a naked skin, a strong fold of which projects outwards around its base. The nostrils are situated near the extremity of the upper surface. There are no true teeth, but their purposes are served by horny prominences, two on each side of each jaw, those in the front narrow, longitudinal, sharp-edged ridges, and those behind broad, j flattened, and molariform. The upper surface of the lateral edges of the mandible has also a number of parallel fine transverse ridges, like those on the bill of a duck. In the cheeks are tolerably capacious pouches, which appear to be used as receptacles for food. The limbs are strong and very short, each with five well- developed toes provided with strong claws. In the foro feet the web not only fills the interspaces between the toes, but extends considerably beyond the ends of the long, broad, and somewhat flattened nails, giving great expanse to the foot when used for swimming, though capable of being folded back on the palm when tho animal is burrowing or walking on the land. On the hind foot the nails are long, curved, and pointed, and the web extends only to their base. On the heel of the male is a strong, curved, sharply pointed, movable horny spur, directed upwards and backwards, attached by its expanded base to the accessory bone of the tarsus. This spur, which attains the length of nearly an inch, is traversed by a minute canal, terminating in a fine longitudinal slit near the point, and connected at its base with the duct of a large gland situated at the back part of the thigh. The whole apparatus is so exactly analogous in structure to the poison gland and tooth of a venomous snake as to suggest a similar function, but evidence that the platypus ever employs its spur as an offensive weapon has, at all events until lately, been wanting. A case is, however, related by Mr Spicer in the Proceedings of the Royal Society of Tasmania for 1876 (p. 162) of a captured platypus inflicting a severe wound by a powerful lateral and inward movement of the hind legs, which wound was followed by symptoms of active local poisoning. It is not improbable that both the inclination to use the weapon and the activity of the secretion of the gland may be limited to the breeding season, and that their purpose may be, like that of the antlers of deer and many similar organs, for combat among the males. In the young of both sexes the spur is present in a rudimentary condition, but it disappears in the adult females. The platypus is aquatic in its habits, passing most of its time in the water or close to the margin of lakes and streams, swimming and diving with the greatest ease, and forming for the purpose of sleeping and breeding deep burrows in the banks, which generally have two orifices, one just above the water level, concealed among long grasses and leaves, and the other below the surface. The passage at first runs obliquely upwards in the bank, some times to a distance of as much as 50 feet, and expands at its termination into a cavity, the floor of which is lined with dried grass and leaves, and in which the eggs are laid and the young brought up. Their food consists of aquatic insects, small crustaceans, and worms, which are caught under water, the sand and small stones at the bottom being turned over with their bills to find them. They appear at first to deposit what they have thus col lected in their cheek pouches, and when these are filled they rise to the surface and quietly triturate their meal with the horny teeth before swallowing it. Swimming is effected chiefly by the action of the broad forepaws, the hind feet and tail taking little share in locomotion in the water. When asleep they roll themselves into a ball, as shown in the figure. In their native haunts they are extremely timid and wary, and very difficult to approach, being rarely seen out of their burrows in the daytime. Mr A. B. Crowther, who has supplemented the often quoted observations of Dr George Bennett upon the habits of these animals in confinement, says, &quot; They soon become very tame in captivity ; in a few days the young