ADAPTATIONS OF ANIMALS
It is not considered necessary to go outside the list of ordinary animals to find sufficient illustrations of adaptations, and it is recommended that attention be given to these during the study of animals prescribed for the regular Course. This may be supplemented by an occasional review of adaptive features for the purpose of emphasizing the general fitness of animals for their varied habits and surroundings. Care must be taken lest the attempt to explain structures by adaptation be carried to an extreme, for it is impossible to account for all the variations in animal forms.
The following list contains a few of the many examples of adaptations to be met with in the Course prescribed for Forms II and III.
The horse walks and runs on the tips of its toes; this gives greater speed.
Wild animals of the cow and deer kind can swallow their food hastily so that they may retire to a safe retreat; there they regurgitate the food and chew it. The domesticated animal retains this habit, though there is no longer a need for it.
The wood-hare's fur is brown in summer, hence its enemies cannot see it against the brown grass and moss; in winter its colour is white, which, against the snow, is a protective colour.
The porcupine is very slow, but its colour and shape make it almost impossible to distinguish from a knot on a log. Its quills form an effective protection when it is discovered.
The feet of the squirrel are adapted for climbing and its teeth for gnawing wood and for opening nuts. The tail serves as a balancing pole for leaping from tree to tree and in winter it acts as a protection from cold.
The earthworm's shape and movements are suited to its habits of burrowing through the soil. Its habits of swallowing the soil fit it for burrowing and for obtaining its food at the same time.
Many insect larvæ, as the tomato worm and the cabbage-worm, are of the same colour as the plants on which they feed, and this enables them to escape detection by birds.
The larvæ of dragon-flies and May-flies breathe in water by means of gills very much as fishes do, but the adult forms are suited for breathing in air.
Female birds are usually dull gray or mottled, so that their colours blend with their surroundings while they are nesting, and hence they do not attract the notice of their enemies.
Birds that swim have webbed feet, which act as oars for pushing them through the water. Their feathers are compact and soft for warmth, and these properties, together with oil on their surfaces, make them waterproof.
The tongue of the woodpecker is long, spear-shaped, and sticky; hence it is adapted for catching insects in the holes pecked into the wood.
The tongue of the toad is fastened at the front end, so that a flap can be shot out for more than an inch in front of the animal, thus enabling it to catch insects on its sticky surface.
The toes of the frog are webbed to make them more serviceable in swimming.
The tail of the musk-rat is strong and broad like the blade of an oar and serves the same purpose as an oar.
The tail of the fish is more serviceable for swimming than legs would be.