Frogs
Prove that frogs and toads are beneficial to man. Did you ever know of a frog or a toad destroying anything useful, or harming any one, or causing warts? How many pupils in class ever had warts? Had they handled frogs before the warts came? Frogs are interesting, gentle, timid animals. Why are they repulsive to some people?
Environment.—Where are frogs found in greatest numbers? What occurs when danger threatens them? What enemies do they have? What colour, or tint, is most prominent on a frog? Does the colour “mimic” or imitate its surroundings? What is the colour of the under side of the body? (Fig. [250].) Why is there greater safety in that colour? What enemies would see water frogs from below? Do tree frogs mimic the bark? The leaves?
Can a frog stay under water for an indefinite time? Why, or why not? What part of a frog is above the surface when it floats or swims in a tub of water? Why? Do frogs croak in the water or on the bank? Why do they croak after a rain? Do toads croak?
Are the eggs laid in still or in flowing water? In a clear place or among sticks and stems? Singly, or in strings or in masses? (Fig. [248].) Describe an egg. Why do frogs dig into the mud in autumn in cold climates? Why do they not dig in mud at the bottom of a pond?
Fig. 250.—Painted Frog (Chorophilus ornatus), of Mexico.
Describe the position of the frog when still (Fig. [250]). Of what advantage in this position? Does the frog use its fore legs in swimming or jumping? Its hind legs? How is the frog fitted for jumping? Compare it in this respect with a jumping insect; a jumping mammal. How is it fitted for swimming? Is the general build of its body better fitted for swimming or for jumping? How far can a frog jump?
External Features.—The frog may be said to have two regions in its body, the head and the trunk. A neck hardly exists, as there is only one vertebra in front of the shoulders (Fig. [252]), while mammals have seven neck (cervical) vertebræ. There are no tail (caudal) vertebræ, even in the tadpole state of frogs and toads.
The head appears triangular in shape when viewed from what direction? The head of a frog is more pointed than the head of a toad. Is the skull a closed case of broad bones or an open structure of narrow bones? (Fig. [252].)