some mammals that have wings but that do not lay eggs. Thus the great families of nature seem to be held together on both sides; just as you keep yourself in a tree by holding on to two different limbs, one with the left hand and one with the right. Bats have wings, as you know, much like the wings of a bird, and much like the fins of a fish, with great spiney ribs running through them. But bats suckle their young just as Mama Dog does her puppies.
Notice how, in still another way, Nature seems to want to make sure that we see that we are all relations and should be kind to one another and find joy in studying each other's lives and in making these lives as happy and helpful as possible.
As we have seen that the lowest forms of life, both animal and vegetable, begin in the water so, in each new class of animals, there is this same grading up. Each begins as a water kind, goes up to land kinds, and then to tree kinds. Among the birds there is the duck that lives most of the time in the water. He swims more than he flies. Then there are the long-legged, long-billed birds that live most of the time on the edge of the water. There are other birds that build their nests in bushes or low trees near the water, and get their food from the seeds that grow on water plants or by catching fish or other water animals. Higher up are other birds that build their nests on the dry land in the meadow far away from the water. Others build in the bushes, higher up; others in low trees; still others in the tallest trees, You know how much brighter a crow in a pine tree is than a goose on a pond.
So with the frogs—water frog, toad, a kind of land frog, and a tree toad; and even a flying frog. Notice the same thing among the rodents; the animals with sharp front teeth, like the two that first appear in baby's mouth. The beaver is a water rodent; the ground squirrel, rat and mouse are ground rodents. Then there is the tree squirrel and the flying tree-squirrel.
Water insects, moist-place insects, dry-land insects, bush insects, tree insects. Water mammals—the whale; "whales" that climb on rocks and get themselves called seals, "sea-lions" or sea-dogs; then our own home dogs. And some of these love water, like the water spaniel and Newfoundland dogs. Some are land dogs, like the fox, the wolf and greyhound. Others of this great dog-toothed, flesh-eating family—the "carnivora"—like the bears, can climb trees. They really do climb trees to get the food that a little insect brother, the bee, gathers and makes over in its own body to feed its
