22 4 AUSTRALIAN AND TASMANIAN ANIMALS 



the skin, the former have entirely disappeared. To protect the lips and nostrils 



when the animal is driving its tunnels through the sand, the muzzle is covered 



with a stout leathery shield. In walking, the marsupial mole rests on the outer 



sides of the fore-feet, and the claws of the third and fourth toes are in consequence 



unusually large and powerful ; the corresponding toes in the hind-limbs curving 



outwards and backwards. The pouch opens backwards. With its feet, aided by 



the stumpy, ringed, and leathery tail, which appears to be pressed against the 



floor, the animal drives a triple sinuous track in the sand, the two outer lines of 



which are more or less interrupted. The marsupial mole inhabits the deserts of 



central South Australia, where rain falls only during a brief portion of the year, 



and is then quickly sucked up in the thirsty dunes and flats, sparsely overgrown 



with porcupine-grass (Trioclia irritans) and acacias. Here it lives almost entirely 



beneath the surface, its galleries running at a depth of some 2 or 3 inches, so that 



it is often possible to track its course by the slight cracking or moving of the 



surface over the position of the underground miner. Above ground the creature 



moves slowly and heavily in a sinuous curve. It enters the ground obliquely ; 



and the hind-limbs are employed to throw the sand backwards in such a manner 



as to fall in again behind the animal, thus leaving no permanent tunnel to mark 



the course. The colour of the marsupial mole almost exactly matches that of the 



sand in which the animal dwells. 



The eye of the marsupial mole, despite the fact that its owner spends so much 



of its time on or near the surface of the ground, is much more completely atrophied 



than in the mole, the optic nerve and lens being wanting, while the other structures 



connected with vision are degenerated in a greater or less degree. The eye itself 



has sunk deep beneath the skin, which passes over it unaltered except for the 



presence of sensory organs developed from the lachrymo-nasal glands and ducts. 



This complete degeneration of the eye may be attributed to the irritating effects of 



the particles of heated sand amid which the creature dwells, the development of 



the glandular structures into sense-organs being in all probability a compensation 



for the loss of vision. 



The largest living herbivorous marsupials are to be found among 

 Kangaroos. . „ 



the kangaroos, or Macropodidce, a group of which all the members, 



despite great specific variation in size, are adapted, by the form of their hind-legs, 



and other peculiarities of structure, for leaping rather than running. In contrast 



to the short and feeble five-toed fore-legs, the hind-legs are of great length and 



strength, and are characterised by the remarkable conformation of the toes, of 



which there are usually four. Of these, the one corresponding to the fourth of the 



typical series of five is extremely large, and furnished with a strong claw ; the outer, 



or fifth, toe, although much smaller than the fourth, is also comparatively stout, 



but the two inner toes (the second and third) are slender and short, and so intimately 



connected with one another by the skin as to afford no assistance to their owner 



in leaping. This extraordinary development of one toe in the leaping marsupials, 



as in a few other swift-footed animals such as the horse and the ostrich, prevents 



a too prolonged contact with the ground, when in rapid motion, and thus adds to 



the speed. The tail, by means of which kangaroos help to support themselves 



while at rest, as a rule is powerfully developed, being long, thick at the root, 



