markable instance of variation in the mode of nest building by the same species. The history of several of our North American birds also affords abundant evidence that it is by no means safe to assume that the same species may not exhibit a great difference in the position and structure of the nest," under varying cir

cumstances.

The recent observations of Dr. James C. Merrill (MSS.) shows that the Icterus cucullatus displays quite as striking variations as this warbler. Some of its nests, like those of the latter, are buried in tangled and elaborately interwoven masses of the Spanish moss, and have no apparent resemblance to others built in the more normal pensile style of its congeners, such as the orchard oriole and others. So, too, with the nests of the Empidonax acadicus. The first identified nest of this species I ever saw was a flat platform, so common in Contopus borealis; and this is its usual style about Philadelphia. The second was a deep cup-like nest, surrounded and surmounted by a curious chevauxde-frise, somewhat in the style of the magpie and the mockingbird. This style is common in Indiana. And now within a few months, I have received two other nests equally well identified, one of them with the eggs, the nests being pensile and not unlike those of the orioles. Such facts as these warn us that we need not and should not, on too slight grounds, discredit either the carefulness or the truthfulness of our fellow-workers in observing the hidden and often varying facts of natural history, even when their observations do not accord with our own. The account of the nesting of the D. dominica given by Mr. Nuttall has always seemed in the last degree improbable, and to be in conflict with that of Mr. Audubon, and their discrepancy has long been a stumblingblock to students until more light began to be thrown upon its history. Mr. Giles' revelations gave us some clue to what seemed the fabulous narrative of Mr. Nuttall. For when we remember how closely together stand the trees in a cypress swamp, how the long "ropes" of Tillandsia do swing from tree to tree, we can now understand how Mr. Nuttall, having never seen it himself, may have imperfectly understood the information he received from another in his account of its swinging nest. And now Mr. Brewster confirms substantially Mr. Audubon's discredited account of his experiences. After all, these pioneers in American ornithology may not have been so absurdly inconsistent, or so entirely at fault as we, in our own ignorance, have taken for granted.

I might go on and prolong this article by other accounts of conspicuous variations made by the same species in its nest-building, citing the lammergeyer that builds indifferently a huge nest on a tall tree, or lays its eggs on the bare ground or some tall cliff, without any nest at all, but I have given enough to show how marked these variations often are. To speculate on the whys and the wherefores would be a very tempting theme were it not that we are so often at fault in attempting to explain them. But I do not believe it is logical to call the intellectual promptings that inspire these variations mere instinct, though we may not be able to read clearly the hidden motives. If experience taught the European martin that its old-fashioned nest, which perchance it had built since the flood, was inconvenient, ill-ventilated and unsafe, and they were prompted by the example of some wiser intellect among themselves to improve upon the hovels of their fathers, so that all at once the whole race made a long stride in improvement, can we call this instinct? Grant that the changes have been slow-extending over fifty years-so gradual that no one has noticed the change while it was going on, we cannot deny the advance, and advance is inconsistent with our ideas of instinct which is unchangeable and incapable of education. It is a clear case of reason and instruction, yielding marked fruits, and is on a higher plane. That birds like the Dendroca dominica and the Icterus cucullatus build a typical nest, like their congeners, where nothing tempts them to do differently, but where the long branches of Tillandsia offer a safe shelter and the absence of labor, shows something higher than instinct, there must be a rational intellect. that prompts them to avail themselves of the opportunity.

If we cannot understand what it can be that stimulates an Empidonax in Staten Island to build a pensile nest, while its fellow in Indiana builds one like a deep cup and surrounded with thorns, and another group in Pennsylvania put theirs on an exposed tree-top, and so flat that the eggs seem liable to roll out, we must see that some cause, hidden to us, is gradually effecting changes that sooner or later may become universal in the species, though which it is to be we may not be able to imagine.

Our eastern song-sparrow's natural instinct prompts it to build on the ground. A series of disasters to its eggs or brood impress it with the need of a safer place. It draws nearer the friendly shelter of a dwelling, and there, no longer on the ground, but up in some thick bush or vine, it makes its nest. For want of the

tufts of grass or weeds that furnished it with a roof, it changes its whole shape and builds a bulky, nearly spherical, domed nest. Some of its offspring adopt the new style of their parents, but others fall back upon their original style. The latter may be considered the promptings of a natural innate instinct, but the domed nests, the changes initiated by the parents and imitated by the more enterprising of their offspring are due to a higher intellectual power that rejects the blind suggestions of their original instinct, and teaches them to follow the paths of experience to safety. This is no imaginary case, but rests on facts within my own observation.

:0:

THE RELATION OF ANIMAL MOTION TO ANIMAL EVOLUTION.

THE

BY E. D. COPE.*

'HE origin of variation in animal structure is, par excellence, the object of the doctrine of evolution to explain. There can be little doubt that the law of natural selection includes the cause of the preservation of certain modifications of preëxistent structure, in preference to others, after they have been brought into existence. In what manner or by what process the growing tissues of young animals have been so affected as to produce some organ or part of an organ which the parent did or does not possess, must be explained by a different set of laws. These have been termed originative, while those involved in natural selection are restrictive only.

I.

Of course we naturally look to something in the "surrounding circumstances" in which a plant or animal is placed, or its "environment," as the most probable stimulant of change of its character, because we know that such beings are totally dependent on cosmic and terrestrial forces for their sustenance and preservation. The difficulty has been to connect these forces with change of structure as originative; to show their operation as multiplying, restricting or destroying organisms already in existence is comparatively easy. This difficulty is partially due

*Abstract of a paper read before the American Association for the Advancement of Science, at Nashville, August, 1877.

to the fact that such modifications must be realized during a limited portion of the life of an animal at least; that is, during the period of growth, when it is not at all or but little subject to the influence of external environment, but is usually protected or supported by the parent.

That the environment and changes in it affect the movements of plants and animals is clear enough. The potency of such changes may be read in the physical history of the earth. A long series of modifications preceded the advent of life upon it, and change, both gradual and sudden, has been exhibited in the configuration and climate of all portions of the surface of the globe since that period. Animals have again and again been called upon to face new conditions, and myriads of species have fallen victims to the inflexibility of their organization which has prevented adaptation to new surroundings. But it is evident that if change of environment has had any influence in the progress of evolution, it has not been alone destructive. It has preceded life as well as death, and has furnished the stimulus to beings capable of change, while it has destroyed those which were incapable of it. It is a truism that change of physical conditions has preceded all great faunal changes, and that the necessity for new mechanism on the part of animals has always preceded the appearance of new structure in geologic times.

The embryology and palæontology of vertebrated animals. show that the primary steps in the progress of this branch of the animal kingdom are marked by the successive changes in the structure of the circulatory system. First we have the various mechanical methods for the aëration of blood in a watery medium; the result being a fluid whose metamorphosis in nutrition produces no heat. After the fishes followed Batrachia, the earliest airbreathers, whose long tarriance to-day in early aquatic stages, is an epitome of the necessarily "amphibious" character of airbreathing vertebrate life, when land and fresh water, in constantly changing areas, were rising and separating from the universal ocean. The successive disappearance of the traces of the fish type of circulation in Batrachia and reptiles, are familiar facts; and the exclusion of the unaërated blood from the systemic circulation in the birds and mammals marks the increase of general temperature which gives those classes one of their claims to superiority.

The appearance of land of course furnished the opportunity

Marine animals

for aquatic animals to assume a terrestrial life. which had acquired the habit of gulping air from the surface, which some of them now possess, perhaps because its richness in oxygen produced an agreeable exaltation or intoxication, would not find visits to the land difficult. And this would naturally follow the necessity of escape from aquatic enemies, or the search for new supplies of food.

In fine, it requires little argument to show that the environment has had in the past as in the present, a primary influence over the movements of animals.

II.

I will now endeavor to exhibit some reasons for believing that the movements of animals affect their structure directly.

There are two alternative propositions expressive of the rela tions of the structures of animals to their uses. Either the use or attempt to use preceded the adaptive structure, or else the structure preceded and gave origin to the use. The third alternative, that use and structure came into being independently of each other is too improbable for consideration in the present article. Many facts render the first of these propositions much the more probable of the two.

A general ground for suspecting that movement affects structure is the fact well known to systematic zoölogists, that adaptive characters are the least reliable in systematic classification, i. e., are the most variable. What we call adaptive characters are those whose teleological significance we can most easily perceive; those whose uses are at the present time most obvious. Systematists habitually fall back on characters which are apparently the least related to the ordinary necessities of the life of the animal, and this not from any theoretical considerations, but because such characters are found to be the most constant; this is a very significant fact, showing as it does that it is the adaptive structures which are undergoing modification to-day. And this truth can doubtless be discerned in all past ages, for many of the structures which are not now more related to the needs of an animal than many others might be, were at one time most essential to its wellbeing, or necessarily related to its environment. Such are the structural characters of the heart and arteries already enumerated. There seems to be no reason why all Vertebrata might not exist with equal comfort and success at the present if possessed of a