Now, notice the frog, which is an amphibian and therefore lower than the reptiles, has not got this quadrate bone, though his companions the newts have; and he seems to tell us that among those old amphibians which roamed in the coal-forests of ages past, there must have been some which,--while they had that great mass of cartilage which imperfect, unborn, milk-giving animals have even now, out of part of which this bone is formed,--yet never went so far as to have the bone itself. If this is so, then here at last, in the distant past--so remote that we cannot even guess how long ago it may have been--we have a point from which the earliest ancestors of the milk-giving animals may have gone off in one direction, and those of reptiles and birds in another. And this would explain how it is that they have so many points in common, while yet the mammalia are without that special bone and other characters which are found both in reptiles and birds.[112] Be this as it may, here is our lowest mammalian form, and he has a relation, the Echidna, very like him in many respects, but who has made a decided step forward; for on the sandy shores and in the rocky gorges of Australia, creatures about a foot long, covered with prickly spines like hedgehogs, and called by the settlers “Porcupine Ant-eaters” (see Fig. 49), shuffle along in the twilight, thrusting out their long thin tongues from the small mouth at the end of their beak-like snout, and feeding on ants and ants’ eggs. These do not belong, however, to the real ant-eater family, but are near relations to the platypus; and they are well protected by their spines in the battle of life, for when attacked they either roll themselves up into a ball like a hedgehog, or burrow down into the sand so fast that they seem to sink into it, leaving only the points of their prickles sticking out to pierce the feet of their enemy. Now these creatures have a little fold of skin under their body, which forms two little pouches over the milk-giving holes, and the little echidna when _very_ tiny is put into this pouch, and keeps its head there while its body grows larger and sticks out beyond. In this way the Echidna can carry her child about with her, and she only turns it out to shift for itself when its prickles are hard and sharp. * * * * * You see, then, that though we began with the simplest known milk-giving animal, we are, in the Echidna, already fairly on our way to the curious pouched creatures of Australia, the “Marsupials,” which, instead of a small fold, have indeed a large pouch of skin, into which they put their little ones when they are less than two inches long, and so imperfect that their legs are mere knobs, and they can do nothing more than hang on to the nipple with their round sucking mouths as if they had grown to it.