the simplification of modes of assault and defense in water and air is replaced here by the most varied motions, such as creeping, running, leaping, climbing, etc., by a diversity of ambushes and hiding-places, and by the necessary adaptation of carnivora to numerous modes of attack, and of herbivora to as numerous modes of escape.
In fact, the specific variations in birds spring from their relations to the surface. Here, as a rule, they seek their food. Here their mental powers arise. Here they develop other functions than flight, other organs than wing-muscles. And it may be that the variations in the fish type spring principally, in like manner, from their relations to the sea-bottom, and the adaptations of carnivorous fish to the powers of escape of forms thus varied.
Thus in the process of animal evolution we reach the dwellers upon the land as the most developed, and the best situated for further development. Those land-animals that retreat to the other fields of life retrograde in consequence. The whales have gone back in their functional development until, in many points, they are affiliated with the fish. The bats have sunk toward the bird-level. So the lowest in function of land-animals are those which retain close affinities with the air and water life of their ancestors, or have but lately migrated to the land. The wingless birds are low in mind and in animal function. The amphibia rest at the lowest level of land-animals. The reptiles are but a step above them.
In the latter class, it is true, there are many which have long broken loose from all connection with a water habitation. Most notable among these are the serpents. But the latter, from their habit of seeking safety in concealment alone, have retrograded functionally, their limbs disappearing, and their bodies being extended prone upon the earth. This location, while an undoubted advantage as affording concealment, is a disadvantage in development. The prone condition of the serpent has caused its limbs to disappear, as useless. Its ribs have taken the place of limbs, and the body has extended in length sufficiently to increase the number of these imperfect limbs, and thus render them more available for motion. Its sensory organs have necessarily become less acute from the disadvantages of position. Gravitation is largely overcome, by the full support of the body upon the earth. But it is replaced by a friction which is equally disadvantageous.
Thus, if we would seek the type of land-animal most likely to develop functionally and mentally, we must look in an opposite direction to that taken by the serpent. The protection that is gained by concealment is a retrograde form. The animals that advance most rapidly are those that are least protected, either by powers of concealment, of flight, or of muscular vigor.
For what does development mean, in its true sense, but extended experience of nature? The greater and more varied the experiences
