ANIMALS UNDERGROUND.
AN interesting find of buried treasure has just been credited to a mole. Coins were seen shining in the earth of a freshly cast-up mole-hill at Penicuick, near Edin. -burgh, and a search showed that the mole had driven his gallery through a hoard of ancient coins of the date of Edward I.
Men of all countries seem agreed in regarding the work of animals underground as something quite normal and common-
place. Perhaps the beet instance of this was the view long held by the Ostiake of North ]Siberia that the mammoths whose bodies and bones they found embedded in the frozen soil were " only " gigantic moles which worked deep down below ground, but were unlucky enough to come too near the top, and so were frozen ! The facts are, however, in very strong contradiction to this view of the subterranean life of animals. Life underground and in the dark is absolutely contrary to the normal habits, tastes, and grim- tare of almost all animals except the very few, like the common moles, taco-taco, and the marsupial sand-moles, which obtain their food below the earth-surface as diving birds catch fish below the sea-surface. It is almost an inversion of their normal way of life, and is probably due to some such compulsion as has also forced many animals to become nocturnal. Nor is it doubtful that if once this necessity were removed their tendency would be to abandon this unnatural life, and return to the regions of light. How strong the pressure must have been which forced them underground may be gathered from the list of English terrestrial mammals. Twelve of these are bats ; but of the remaining twenty. nine no less than sixteen, or more than half, live either wholly or partly underground. The list includes the fox, three shrews, the mole, the badger, the otter, three species of mice, two rats, three voles, and the rabbit. Besides there are several species of birds, as widely different in habit as the stormy petrels, sand-martins, puffins, sheldrake ducks, and the kingfisher, which for a time live in holes excavated in the earth. To abandon the sun, to bask in whose rays is to most animals one of the most agreeable of physical enjoy- ments, is an almost greater sacrifice than the relinquish- ment of fresh air. Yet the sacrifice is made, and the creatures, though not without occasional suffering and loss of health directly attributable to this cause, have succeeded in adapting themselves with great success to the new conditions. It might well be that the measure of this success decreased in proportion to the completeness with which the different species have adopted the underground habit and abandoned light and air. Bat in normal conditions this is not the case. The fox, whom we take to be the last of English mammals to become a burrower and dweller in holes—largely owing to the increase of foxhnnting and multiplication of packs of hounds —is an animal which spends as little time there as it can help, and has never ceased to suffer in health from the change. The earths become tainted, the foxes contract mange, and the spread of this fatal disease has increased yearly as they have become more subterranean, and by taking their food into the earths have converted them into larders as well as sleeping-places. How most of the burrowing animals find life endurable at all is difficult to discover. No one who has seen colliers coming for their lamps and about to descend into the pit can have failed to note the marks of physical strain exhibited by all, from old men to boys. As each man or lad comes up and shouts the number of his lamp, the harsh loud voices, the over-wrought lines of the face, and the general air of tension show that, however well satisfied the pitman is with his calling, he at least is not yet adapted to the underground life. But burrowing animals are among the merriest of the merry ; there are few creatures more full of gaiety and buoyant spirits than a prairie-dog, or even a sandhill-rabbit ; and we have only once seen an animal grimy from attempted burrowing, and that was an opossum which mistook a chimney for a hole in a hollow tree. Some have coats so close and fine that sand runs off them like water does from feathers; others have " shivering muscles," by which they can shake their jackets without taking them off. Rats, however, do object to some forms of dust, and will not burrow in it. An old Suffolk rat- catcher always laid ashes in the runs made by them beneath brick floors. His theory on the subject was that the ashes "fared to make them snuffle." But even if earth, dust, and clay do not adhere to the animals' coats when burrowing, the danger, or at least the discomfort, to the delicate surface of the eye would seem to afford an almost constant source of uneasiness to creatures burrowing in loose soil. But the eyes of most burrowing creatures are by no means protected against such damage. If the rat and the rabbit had a horn plate over their eyes, as a snake has, or overhanging eyebrows and deeply sunk orbits, the modification would be at once explained by evolution ; but they exhibit no such modification whatever. On the contrary, both of them have prominent, rather staring eyes, without protection, and no eyelashes to speak of. We believe that, just as divers learn to keep their eyes open under water without feeling pain, 'so many of the mining animals can endure the presence of dust and grit on the eye without discomfort. Tame rats will allow duet or fine sand to rest on the eyeball without trying to remove it ; and it may be inferred that rabbits, mice, voles, and shrews can do the same. The mole's eyes •have become so atrophied, that when a mole is skinned the eyes come of with the skin ; but this is probably not 'because the mining hurts the eye, but because the mole, having learnt to work by scent and touch, had little further -use for sight.
Ventilation, or rather the want of it, must be another diffi- culty in the underground life of almost all mammals. The rabbit and the rat secure a current of air by forming a bolt- hole in connection with their system of passages; but the fox, the badger, and many of the field voles and mice seem indifferent to any such precaution. There is no doubt that whatever gave the first impulse to burrow, many animals look upon this, to us, most unpleasant exertion as a form of actual amusement. It also confers a right of property. Prairie- dogs constantly set to work to dig holes merely for the love of the thing. If they cannot have a suitable place to exercise their talent in, they will gnaw into boxes or chests of drawers, and there burrow, to the great detriment of the -clothes therein contained. In an enclosed prairie-dog "town" they have been known to mine until the superincumbent earth collapsed and buried the greater number. A young prairie- -dog let loose in a small gravel-floored house instantly dug a hole large enough to sit in, turned round in it, and bit the first person who attempted to touch him. Property gave him -courage, for before he had been as meek as a mouse. It is noticeable that the two weakest and least numerous of our mice, the dormouse and the harvest-mouse, do not burrow, but make nests ; and that these do not multiply or maintain their numbers like the burrowing mice and voles. But the tact that there are members of very closely allied species, some of which do burrow, while others do not, seems to indicate that the habit is an acquired one. In this connection it is worth noting that many animals which do not -burrow at other times, form barrows in which to conceal and protect their young, or, if they do burrow, make a different kind of a more elaborate character. Among these nursery burrows are those of the dog, the fox, the sand-martin, the kingfisher, and the sheldrake. Fox-hound litters never do so well as when the mother is allowed to make a burrow on the sunny side of a straw stack. In time .she will work this 5 ft. or 6 ft. into the stack, and keep the puppies at the far end, while she lies in the entrance. Vixens either dig or appropriate a clean burrow for their cubs, which is a natural habit, or, at any rate, one acquired previously to the use of earths by adult foxes.
The sand-martins are, however, the most complete examples -of creatures which have taken to underground life entirely to protect their young, and abandon it with joy the instant these have flown. How far the kingfisher and the sheldrake con- tribute to the making of the burrows in which they lay their eggs is doubtful, but it is a very notable change of habit in birds of such strong flight and open-air, active habits. It may be paralleled by the case of the stormy petrels and fork- tailed petrels, true ocean birds, which, nevertheless, abandon the sea and air to dig deep holes in the soil of the Hebridean islets, and rear their young in these dark and tortuous passages. Rabbits, rats, and some other rodents make a nursery burrow of a very rudimentary kind, having only one opening which the mothers close up when leaving the nest. This probably gives the clue to the process by which the true "underground animals" have been evolved. First they scratched holes in which to shelter their young. Then they made use of the same device to pro- tect themselves, and acquired mach greater skill in work- ing, and some modifications of coats and claws to do this with comfort and effect. In time the habit became so easy 'that its exercise afforded them pleasure; and thus we have the spectacle of the prairie-dog who digs holes for amuse- ment. Another primitive instinct may also have contributed to develop the burrowing habit, that of burying food. Dogs will scratch rudimentary barrows to do this, and there is no doubt that the rats, hamsters, field-voles, and other rodents felt the burrowing impulse in this connection. Some tame rats kept in a cage where they could not burrow were recently seen to cover their food up with small pebbles which they fetched from the floor, but had it been possible to make a hole and so secrete it, they would no doubt have done so.
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