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lower depth there is no difference between winter and summer, and still lower none between day and night. The bassalian fishes inhabit a region of great cold and inky darkness. Their bodies are subjected to great pressure, and the conditions of life are practically unvarying. There is, therefore, among them no migration, no seasonal change, no spawning season fixed by outside conditions, and no need of adaptation to varying environment. As a result, all are uniform indigo-black or purple in color, and all show more or less degeneration in those characters associated with ordinary environment. Their bodies are elongate, from the lack of specialization in the vertebræ. The flesh, being held in place by the great pressure of the water, is soft and fragile. The organs of touch are often highly developed. The eye is either excessively large, as if to catch the slightest ray of light, or else it is undeveloped, as if the fish had abandoned the effort to see. In many cases luminous spots or lanterns are developed by which the fish may see to guide its way, and in some forms these shining appendages

some format he shining appemiages are highly developed. In one form (Æthoprora) a luminous body covers the end of the nose, like the headlight of an engine. Many of these species have excessively large teeth, and some have been known to swallow animals actually larger than themselves. Those which have lanternlike spots have always large eyes.

The deep-sea fishes, however fantastic, have all near relatives among the shore forms. Most of them are degenerate representatives of well-known types-for example, of eels, cod, smelt, grenadiers, sculpin, and flounders. The deep-sea crustaceans and mollusks are similarly related to shore forms.

The third great subdivision of marine animals is the littoral or shore group, those living in water of moderate depth, never venturing far into the open sea either at the surface or in the depths. This group shades into both the preceding. The individuals of some of the species are excessively local, remaining their life long in tide pools or coral reefs or piles of rock. Others venture far from home, becoming more or less pelagic. Still others ascend rivers either to spawn (anadromous, as the salmon, shad, and striped bass), or for purposes of feeding, as the robalo, corvina, and other shore fishes of the tropics. Some live among rocks alone, some in seaweed, some on sandy shores, some in the surf, and some only in sheltered lagoons. In all seas there are fishes and other marine animals, and each creature haunts the places for which it is fitted.

There is the closest possible analogy between the variations of species of animals or plants in different districts and that of words in different languages. The language of any people is not a unit. It is made up of words which have at various times and under various conditions come into it from the speech of other people. The grammar of a language is an expression of the mutual relations of these words. The word as it exists in any one language represents the species. Its cognate or its ancestor in any other language is a related species. The words used in a given district at any one time constitute its philological fauna. There is a struggle for existence between words as among animals. For example the words begin and commence, shake and agitate, work and operate (Saxon and French) are in the English language constantly brought into competition. The fittest, the one that suits English purposes best, will at last survive. If both have elements of fitness, the field will be divided between them. The silent letters in words tell their past history, as rudimentary organs tell what an animal's ancestry has been. This analogy, of course, is not perfect in all regards, as the passing of the words from mouth to mouth is not rigidly comparable with the generation of animals.

We may illustrate the formation of species of animals by following any widely used word across Europe. Thus the Greek aster becomes in Latin and Italian stella; whence the Spanish estrella and the French étoile. In Germany it becomes Stern, in Danish Stjern; whence the Scottish starn and English star.

In like manner, the name cherry may be traced from country to country to which it has been taken in cultivation. Its Greek name, kerasos, becomes cerasus, ceresia, ceriso, cereso, cérise, among the Latin nations. This word is shortened to Kirsch and Kers with the people of the North. In England, cherys, cherry, are obviously derived from cérise.

The study of a fauna or a flora as a whole is thus analogous to the study of a living language. The evolution of a language corresponds to the history of the life of some region. Philology, systematic zoology, and botany are alike intimately related to geography. The parallelism between speech districts and faunal districts has been many times noted. The spread of a

language, like the spread of a fauna, is limited by natural barriers. It is the work of civilization to break down these barriers as limiting the distribution of civilized man. The dominant languages cross these barriers with the races of man who use them, and with them go the domesticated animals and plants and the weeds and vermin man has brought unwillingly into relations of domination.

The profitable study of the problems of geographical distribution is possible only on the theory of the derivation of species. If we view all animals and plants as the results of special creations in the regions assigned to them, we have instead of laws only a jumble of arbitrary and meaningless facts. In our experience with the facts of science we have learned that no fact is arbitrary or meaningless. We know no facts which lie beyond the realm of law. We may close with the language of Asa Gray:

"When we gather into one line the several threads of evidence of this sort we find that they lead in the same direction with the views furnished by other lines of investigation. Slender indeed each thread may be, but they are manifold, and together they bind us firmly to the doctrine of the derivation of species."

CHAPTER XVI

ADAPTATIONS

It is a wise provision of nature that trees shall not grow up into the sky.-Gorth E.

The adaptation of every species of animal and plant to its environment is a matter of everyday observation. So perfect is this adaptation in its details that its main facts tend to escape our notice. The animal is fitted to the air it breathes, the water it drinks, the food it finds, the climate it endures, the region which it inhabits. All its organs are fitted to its functions: all its functions to its environment. Organs and functions are alike spoken of in a half-figurative way as concessions to environment. And all structures and powers are in this sense concessions, in another sense, adaptations. As the loaf is fitted to the pan, or the river to its bed, so is each species fitted to its surroundings. If it were not so fitted, it would not live. But such fitness on the vital side leaves large room for variety in characters not essential to the life of the animal. Thus we ascribe nonessential characters to variation, preserved by heredity and guarded by isolation. Vital or adaptive characters originate in the same way, but these are preserved in heredity and guarded and intensified by selection.

The strife for place in the crowd of animals makes it necessary for each one to adjust itself to the place it holds. As the individual becomes fitted to its condition, so must the species as a whole. The species is therefore made up of individuals that are fitted or may become fitted for the conditions of life. As the stress of existence becomes more severe, the individuals fit to continue the species are chosen more closely. This choice is the automatic work of the conditions of life, but it is none the less effective in its operations, and in the course of centuries it may be considered unerring. When conditions change, the perfection of adaptation in a species may be the cause of its extinction. If the need of a special fitness cannot be met, immediately the species will disappear. For example, the native sheep of England have developed a long wool fitted to protect them in a cool, damp climate. Such sheep, transferred to Cuba, died in a short time, leaving no descendants. The warm fleece, so useful in England, rendered them wholly unfit

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Fig. 188. --Nest of Vespa, a social wasp. (Photograph by A. L. Melander and C. T. Brues.)

for survival in the tropics. It is one advantage of man, as compared with other forms of life, that so many of his adaptations are external to his structure, and can be east aside when necessity arises. The great fact of nature is adaptation. But while general adaptation to widespread conditions is universal, there exist also a multitude and variety of special adaptations fitting organisms to special conditions. These special adaptations arrest our attention to a greater degree than general adaptations because they furnish the element of contrast. The various types of special adaptations may be roughly divided into five classes as follows: (a) Food-securing; (b) self

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