2. External characters.—Catch a frog; is its body dry or moist? Does it feel cold or warm? How does it behave when caught? Does it soon become tame if well treated? Put a frog under an inverted pickle-bottle and observe it carefully. What is its size? What was the size of the smallest frog you have seen? At what time of the year can the smallest frogs be seen? What is the colour of the frog? Put one frog with dark-coloured leaves and soil, and another with light-coloured leaves, and try to find out if the skin of the first becomes lighter and that of the second darker in colour. Is it an advantage to the frog to be able to change slightly in colour? Why? What is the position of the frog when at rest? Notice the shortness of the body, the hump on the back, the relative lengths of the limbs, the 4 unwebbed fingers, the 5 webbed toes, and the absence of a tail. What is the advantage of the long hind-limbs? Mention other leaping animals whose hind-limbs are [Pg 333] longer than the fore-limbs. Is a short-bodied animal (i.e. one with its four limbs pretty close together) less likely to be injured by the fall, after a leap, than a long-bodied animal? Why? Put the frog into water, and watch it swim. What is the use of the webs between the toes? Examine the head. Notice the very wide stretch of the mouth, the small openings of the nostrils, the large prominent eyes, and the ear-drum—a dark-coloured disc on each side, a little below and behind the eye. 3. Breathing.—Watch the up-and-down movements of the floor of the mouth, by which the animal pumps air, through its nostrils, in and out of its mouth-cavity. 4. Method of feeding.—Put live insects, small worms, etc., under the upturned bottle enclosing the frog, and watch the animal’s method of feeding. Try to see how it uses its tongue. What is the advantage of the wide gape of the mouth? Can you get the frog to accept dead insects? 5. The inside of the mouth.—To kill a frog painlessly, soak about a teaspoonful of chloroform on cotton wool, and put it with the frog under a bottle or tumbler. After 15 or 20 minutes the frog will be quite dead.