middle of Sweden was submerged, and the Baltic was a great gulf of the Glacial Ocean, and not connected with the German Ocean. By the gradual elevation of the Scandinavian Continent, the Baltic became disconnected from the Glacial Ocean, and the great lakes separated from the Baltic. In consequence of the gradual change of the salt water into fresh, the marine fauna became gradually extinct, with the exception of the glacial forms mentioned above."

It is possible that the presence of marine types in our Great Lakes is to be regarded as due to some depression of the land which would connect their waters with those of the Gulf of St. Lawrence. On this point, however, our data are still incomplete.

To certain species of upland or mountain fishes, the depression of the Mississippi basin itself forms a barrier which cannot be passed. The Blackspotted Trout,1 very closely related species of which abound in all waters of northern Asia, Europe, and western North America, has nowhere crossed the basin of the Mississippi, although one of its species finds no difficulty in passing Behring Strait. The Trout and White-fish of the Rocky Mountain region are all species different from those of the Great Lakes or the streams of the Alleghany system. To the Grayling, the Trout,

1 Salmo fario L., in Europe; Salmo labrax Pallas, etc., in Asia; Salmo gairdneri Richardson, in streams of the Pacific Coast. Salmo mykiss Walbaum, in Kamtschatka, Alaska, and throughout the Rocky Mountain range to the Mexican boundary, and the head-waters of the Kansas, Platte, and Missouri.

the White-fish, the Pike, and to arctic and subarctic species generally, Behring Strait have evidently proved no serious obstacle to diffusion; and it is not unlikely that much of the close resemblance of the fresh-water fauna of northern Europe, Asia, and North America is due to this fact. To attempt to decide from which side the first migration came in regard to each group of fishes might be interesting; but without a wider range of facts than is now in our possession, such attempts would be mere guesswork and without value. The interlocking of the fish-faunæ of Asia and North America presents, however, a number of interesting problems, for numerous migrations in both directions have doubtless taken place.

I could go on indefinitely with the discussion of special cases, each more or less interesting or suggestive in itself, but the general conclusion is in all cases the same. The present distribution of fishes is the result of the long-continued action of forces still in operation. The species have entered our waters in many invasions from the Old World or from the sea. Each species has been subjected to the various influences implied in the term "natural selection," and under varying conditions its representatives have undergone many different modifications. Each of the six hundred species we now know may be conceived as making every year inroads on territory occupied by other species. If these colonies are able to hold their own in the struggle for possession, they will multiply in the new conditions, and the range of the species becomes widened. If the surroundings are different,

new species or varieties may be formed with time; and these new forms may again invade the territory of the parent species. Again, colony after colony of species after species may be destroyed by other species or by uncongenial surroundings.

The ultimate result of centuries on centuries of the restlessness of individuals is seen in the facts of geographical distribution. Only in the most general way can the history of any species be traced; but could we know it all, it would be as long and as eventful a story as the history of the colonization and settlement of North America by immigrants from Europe. But by the fishes each river in America has been a hundred times discovered, its colonization a hundred times attempted. In these efforts there is no co-operation. Every individual is for himself, every struggle a struggle of life and death; for each fish is a cannibal, and to each species each member of every other species is an alien and a savage.

THE NOMENCLATURE OF AMERICAN

FEW

BIRDS.1

EW scientific books of recent years have been awaited with so much interest as the "CheckList" of birds and its accompanying "Code," published by the American Ornithologists' Union. To those interested in systematic ornithology the work is, of course, of the highest importance, as giving an authoritative settlement, so far as authority can settle anything in science, of the much-vexed questions in bird nomenclature. But to the systematic workers in other departments of zoology, and even to botanists, its interest is scarcely less great. For we who work in other fields are very willing to recognize the fact that the great questions which underlie all systematic nomenclature must be first met and settled by the ornithologists. The abundance and attractiveness of birds, and the ease with which they may be collected and studied, have combined to render ornithology one of the best cultivated of all departments of science. In spite of a good deal of crude or "amateur" work, which, in one way or another, gets published, it is, I think, not too much to say that in all the various matters which make up the groundwork of systematic science- in the discrimination

1 A Review of the "Code of Nomenclature and Check-List of the American Ornithologists' Union.”

of species and varieties, in the study of the relations of these groups to each other and to their environment - American ornithology stands in the very front of systematic science.

We may therefore, in the various stages through which our ornithology has passed or is passing, read the future history of our own branches of science. In many regards the ornithologists are fighting our battles for us, and we may take advantage of the results won by their efforts. Thus the discussion of climatic influences on the character of species, first seriously taken up by Mr. Joel A. Allen in 1871, which has culminated in the trinomial system of nomenclature, has relieved workers in other fields from the need of urging the same considerations. As soon as our facts are sufficient for us to use the trinomial system, we shall find it ready for our service, perfected in all its details. Again, the absolute importance of the law of priority has impressed itself on the ornithologists in spite of themselves; for in past times the students of birds have been among those who have most sinned against this law. The efforts of Cassin, Coues, Stejneger and others to ascertain the facts in regard to old names, have shown that no possible middle ground exists between chaos and law in matters of nomenclature. It is quite true, as the authors of the "Code" have insisted, that “nomenclature is a means and not an end in science." But the experience of ornithologists has shown us that in systematic zoology and in zoögeography, this means is one absolutely essential to any end of importance. A system of