of the length of the head of such a whale, so that the difference in size between the duck's lamellæ and the imperfect baleen-plates of this whale is not markedly disproportionate, after all. After the examination of the beaks of various species of swimming-birds, Mr. Darwin arrives at the conclusion that "a member of the duck family with a beak constructed like that of the common goose, and adapted solely for grazing, or even a member with a beak having less well-developed lamellæ, might be converted by small changes into a species like the Egyptian goose (which partly grazes and partly sifts mud)—this into one like the common duck—and, lastly, into one like the shoveler, provided with a beak almost exclusively adapted for sifting the water; for this bird could hardly use any part of its beak, except the hooked tip for seizing or tearing solid food. The beak of a goose, as I may add," says Mr. Darwin, "might also be converted by small changes into one provided with prominent recurved teeth, like those of the Merganser (a member of the same family), serving for the widely different purpose of securing live fish."
Mr. Darwin next endeavors to apply the moral of this interesting sketch of probable modification of the bills of ducks to the case of the whales. If the stages of modification in these animals are hypothetically so clear, may not the case of the whalebone-bearing whales be susceptible of like explanation? A certain whale (Hyperoödon) belonging to a small group known popularly as the "beaked whales," from the possession of a prominent beak or snout, has no true teeth, but bears rough, unequal knobs of horny nature in its palate. Here, therefore, is a beginning for the work of selection and development. Granted that these horny processes were useful to the animal in the prehension and tearing of food, then their subsequent development into more efficient organs is a warrantable inference if the order of living nature teaches us aright. From rudimentary knobs, a further stage of development would lead to an increase in which they may have attained the size of the lamellæ of an Egyptian goose, which, as already remarked, are adapted both for sifting mud and for seizing food. A stage beyond, and we reach the shoveler's condition, "in which the lamellæ would be two thirds of the length of the plates of baleen," in a species of whalebone whale (Balænoptera) possessing a slight development of these organs. And from this point, the further gradations leading onward to the enormous developments seen in the Greenland whale itself, are easily enough traced. Hypothetically, therefore, the path of development is clear enough. Even if it be remarked that the matter is entirely one of theory, not likely to be ever partly verified, far less proved at all, we may retort that any other explanation of the development of the organs of living beings, and of living beings themselves, must also be theoretical in its nature and as insusceptible of direct proof as are Mr. Darwin's ideas. But the thoughtful mind must select a side, and choose between probabilities;
