Disappearing Ears and Legs

Ears

But the ear is different.

Sound* is set in motion by the shock or the vibration of bodies.

This transfers to the ears the impression it has received, penetrates everywhere, and moves through every medium, even the masses of the densest bodies.

The result is that every animal which is part of an organic structural design in which the ear is an essential part always has the opportunity to exercise this organ in whatever place it dwells.

Thus, vertebrates all have ears.

If the ears are lacking, the subordinate classes of that animal also lacks ears.

Disappearance of Legs

Finally, part of the organic structural design of reptiles, as in other vertebrate animals, includes having four limbs dependent on their skeleton.

Consequently, snakes should have four of them, especially since they do not make up the last order of reptiles and since they are more distant from the fish than are the batrachians (frogs, salamanders, and so on).

However, snakes took up the habit of crawling on the ground and hiding in the grass.

Thus, their body, as a result of constant and repeated efforts to extend itself, so as to pass into narrow spaces, acquired a considerable length, totally disproportionate to its size.

Limbs would have been really useless to these animals and consequently remained unused (for extended limbs would have been an impediment to their need to crawl, and very short limbs, necessarily four in number, would have been incapable of moving their bodies).

Thus the lack of use of these parts, remaining constant for the races of this animal, made these very parts disappear entirely, although the limbs were actually in the design of the organic structure of animals of their class.

Many insects which, according to the natural characteristics of their order and even their genus, should have wings, lack them more less completely, because they do not use them.

A number of coleoptera, orthopetera, hymenoptera, and hemiptera, and so on give us examples of this fact. The habits of these animals never put them in situations where they used their wings.

But it is not sufficient to provide an explanation for the cause which has led to the state of the organs of different animals, a condition which we observe is always the same in those of the same species.

In addition, it is necessary to make known the alterations brought about in the organs of a single individual during its lifetime, solely as the product of a great mutation in the habits unique to the individuals of its species.

Mr. Tenon of the Institute examined the intestinal canal of several men who had been passionate drinkers for most of their lives.

He constantly found the organ shortened by an extraordinary amount compared with non drinkers.

Those addicted to drinking eat very little solid food.

The drink which they consume in abundance is frequently sufficient to nourish them.

The spirit drinks do not stay long in the stomach or the intestine.

Such drinkers would have their stomach and the rest of the intestinal canal lose the habit of being distended, just as the stomachs of sedentary persons constantly busy with intellectual work who are accustomed to eating only a little gradually over time contract, and their intestines grow shorter.

This matter is not at all a question of a shrinking and a contraction brought about by a gathering in of the parts which would allow for an ordinary extension if these internal organs were filled, rather than undergoing a sustained emptiness.

It is rather a question of a real and considerable shrinkage and contraction such that these organs would break rather than yield suddenly to causes which demand an ordinary extension.

Compare, at entirely similar ages, a man who, in order to free himself for studies and habitual intellectual work, has acquired the habit of eating very little with another who habitually takes plenty of exercise, frequently goes out of his house, and eats well.

The stomach of the first will have little capacity.

• It will be filled by a very small quantity of nourishment

The stomach of the second will have preserved and even increased its capacity.

There we have an organ strongly modified in its dimensions and capacity by the single cause of a change in habits over the lifetime of an individual.

The frequent use of an organ, once it becomes constant and habitually, increases the capacities of this organ, develops it, and makes it acquire dimensions and an active power which the organ does not possess in the animals which exercise it less.

It has just been shown that the lack of use of an organ which ought to exist modifies it, diminishes it, and ends up destroying it.

The continuous use of an organ, along with the efforts made to derive from it a substantial benefit in circumstances which demand it, fortifies the organ, extends and enlarges it, or makes new organs from it which can carry out functions which have become essential.

The bird drawn to water by the need to to find there prey which sustains its life extends the digits on its feet with which it wishes to strike the water and move on the surface.

The skin which unites these digits at their base, because of these constantly repeated separations of the digits, acquires the habit of stretching itself.

Thus, over time, the large membranes which link the digits of ducks, geese, and so on are formed just as we see them. The same efforts made for swimming, that is, to push the water in order to advance and move in this liquid have in the same manner extended the membranes between the digits of frogs, sea-tortoises, otter, beaver, and so on.

By contrast, the bird whose way of living accustoms it to perching in trees and which descends from individuals which have all acquired this habit, necessarily has longer digits on its feet shaped in a different way from those of the aquatic animals which I have just cited.

Its claws, over time, grow longer, sharper, and hook-like to grasp the branches on which the animal rests so often.

The shore bird which has no inclination to swim but needs to approach the water’s edge to find its prey constantly runs the risk of sinking down in the mud.

This bird wishes that its body does not sink in liquid.

It makes every effort to extend and lengthen its feet.

This long habit which this bird and all those of its race acquire of extending and lengthening their feet brings it about that the individuals of this race find themselves elevated as if on stilts, having gradually developed long bare legs, that is, legs without feathers up to the thighs and often further than that.

The same bird, wishing to fish without getting its body wet, is required to make continual efforts to lengthen its neck.

The consequences of these habitual efforts in this individual and in those of its race must have, over time, lengthened their necks remarkably, a point which is, in fact, confirmed by the long neck of all shore birds.

If some swimming birds, like the swan and the goose, in which the legs are short, have nonetheless a very long neck, the reason is that these birds, while moving along on the water, are accustomed to plunge their heads down into it as deeply as they can to take from there the aquatic larvae and different animalcules on which they feed. They make no effort to lengthen their limbs.

If an animal, in order to satisfy its needs, makes repeated efforts to lengthen its tongue, that organ will acquire a considerable length (anteater, green woodpecker).

If the animal needs to seize something with this same organ, then its tongue will divide and become forked. The tongue of the humming birds, who seize things with their tongue, and that of lizards and snakes, who use their tongues to feel and recognize the bodies in front of them prove what I am proposing.