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The length of the animal when full grown is from 18 to 20 in. 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 is 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

(From Gould's Mammals of Australia.)

Platypus.

surface. There are no true teeth in the adult, although the young possess a set which are shed after being worn down by friction with food and sand, their purposes being afterward served by horny prominences, two on each side of each jaw—those in the front narrow, longitudinal, sharp-edged ridges, and those behind broad, 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 short, each with Eve well-developed toes provided with strong claws. In the fore feet the web not only fills the inter spaces 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 bei11g folded back on the palm when the 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, and there is now evidence that it employs this organ as an offensive weapon.

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 grass and leaves, and the other below the surface. The passage at first runs obliquely upwards in the bank, sometimes to a. distance of as much as 50 ft., and expands at its termination into a cavity, the floor of which is lined with dried grass and leaves, and in which, it is said, the eggs are laid[1] 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 collected 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 supplemented the often quoted observations of Dr George Bennett upon the habits of these animals in confinement, states: “They soon become very tame in captivity; in a few days the young ones appeared to recognize a call, swimming rapidly to the hand paddling the water; and it is curious to see their attempts to procure a worm enclosed in the hand, which they greedily take when offered to them. I have noticed that they appear to be able to smell whether or not a worm is contained in the closed hand to which they swim, for they desisted from their efforts if an empty fist was offered.”  (W. H. F.; H. Sc.) 

  1. Some doubt has been expressed as to whether the eggs are extruded or hatched within the body. At a scientific meeting of the Zoological Society of London, on the 17th of December 1901, Mr Oldfield Thomas read a letter from Mr G. Metcalfe, who had lived many years in a region inhabited by these animals. He had made special inquiries of the authorities of the Sydney, Melbourne, Brisbane and Hobart museums, and published questions in the newspapers, but no evidence has reached him that the eggs of Ornithorhyncus have ever been obtained except by the dissection of the mother. Mr Thomas laid stress on what had been advanced on the other side by Mr Caldwell (Philosophical Transactions, clxxviii. 463), Professor Spencer (Nature, xxxi. 132) and Mr J. Douglas Ogilby (Catalogue of Australian Mammals, p. 1, Sydney, 1902), but expressed the hope “that further inquiries might be made by naturalists in Australia as to the actual finding of such eggs in the burrows, so that this most interesting point might be finally settled.”