Fig. 248.—Metamorphoses of the Frog, numbered in order.
Do eggs hatch and tadpoles grow more rapidly in a jar of water kept in a warm place or in a cold place? In pond water or in drinking water? Can the tadpoles be seen to move in the eggs before hatching? When do the external gills show? (Fig. [248].)
Fig. 249.—Tadpole, from below, showing intestine and internal gills. (Enlarged.)
What parts may be described in a tadpole? What is the shape of the tail? Compare the tadpole with the fish as to (1) general shape, (2) covering, (3) fins, (4) tail, (5) gills.
Do the external gills disappear before or after any rudiments of limbs appear? (6, 7, Fig. [248].) Can you locate the gills after they become internal? (Fig. [249].)
In what state of growth are the legs when the tadpole first goes to the surface to breathe? Which legs appear first? Of what advantage is this? What becomes of the tail? Is the tail entirely gone before the frog first leaves the water? Are tadpoles habitually in motion or at rest?
Is the intestine visible through the skin? (Fig. [249].) Is it straight or coiled? Remembering why some fish have larger intestines than others, and that a cow has a long intestine and a cat a short one, state why a tadpole has a relatively longer intestine than a frog.
Compare the mouth, jaws, eyes, skin, body, and habits of tadpole and frog.