Meanwhile the tadpole’s lips are gradually forming into a round mouth, much like the lamprey’s, and by-and-by the inner part of this mouth is covered with two little horny jaws, forming a sharp beak (3, Fig. 15) with which he will nip off pieces of weed for food. Meanwhile, as he grows larger and larger, and eyes, nostrils, and flat ears form in the head, a covering begins to grow back over the sides of the neck, and little by little the branching tufts disappear (3, Fig. 15). How, then, can he breathe now? Watch carefully and you will see that he gulps every moment as we saw the minnow doing (p. 23). The fact is that the outside tufts have faded away, and under the cover the tadpole has six slits in his throat, like the slits of the lamprey, which are covered in somewhat similar fashion to those of the amphioxus (see p. 11), and he breathes through them. Here is our tadpole, then, to all intents and purposes a fish. He swims with a fish’s tail; he gulps in water at his mouth, passing it out at the slits in his throat after it has poured over his fish’s gills. Moreover, he has a fish’s heart, of two chambers only, like the minnow’s (p. 23), which pumps the blood into these gills to be freshened, while, like the lamprey, he has a gristly cord, enlarged at the end to form a gristly skull, a round sucking mouth, and no limbs. All this time, however, though he has a fish’s fin round his tail, he has no arm or leg fins. Wait a while and you will see that under his tender skin far more useful limbs are being prepared. As he grows bigger and more active week by week, wriggling among the weeds and feeding greedily, two little bumps appear one on each side of his now bulky body, just where it joins the tail. These bumps grow larger every day, until, lo! some morning they have pierced through the skin, and two tiny hind legs (4, Fig. 15) are working between the body and the tail. The two front legs are longer in coming, for they are hidden under the cover which grew over the gills, but in about another week they too appear, and we have a small four-legged animal with a lamprey’s tail (5, Fig. 15). These legs are something far in advance of fish fins, for they have shoulders and thighs, arm and leg bones, wrist and ankle bones, hand and foot bones; and instead of the large number of rays in a fish’s fin they have four fingers on their short front legs, and five toes at the end of long hind ones; the toes being joined together by a web, which helps him wonderfully in striking the water as he swims.