in cloudy, wet weather. They return to ponds and brooks in spring at the time for laying eggs. This time for both frogs and toads is shown by trilling. All frogs, except tree frogs, remain in or near the water all the year.
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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 drinking water? Can the tadpoles be seen to move in the eggs before hatching? When do the external gills show? (Fig. 248.)
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.)
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Fig. 249.—Tadpole, from below, showing intestine and internal gills. (Enlarged.)
