Page:Popular Science Monthly Volume 15.djvu/254

242 and scales of these animals. To what conclusion, then, does this same principle lead us respecting the nature of the baleen-plates in the mouth of the Greenland whale and its allies? To a sufficiently certain, but at the same time startling thought, is the reply of the comparative anatomist.

If we examine the structure of the human mouth, or that of animals allied to man, we find that cavity to be lined by a delicate layer named epithelium. This epithelium consists really of a modification of the upper layer of the skin, and we see this modification familiarly in the difference between the skin of the face and the layer which is infolded to form the covering of the lips and the lining membrane of the mouth. No tissue is more familiar to the student of physiology than epithelium, composed as it is of epithelial cells or microscopic elements, which in one form or another are found in almost every important tissue of the body. The epithelium is a delicate tissue, as usually seen in man and vertebrate animals; but in some instances it becomes hardened by the development of horny matter, and may then appear as a tissue of tolerably solid consistence. In the mouth of a cow or sheep, the epithelium of part of the upper jaw is found hardened and callous, and there forms a horny pad against which the front teeth of the lower jaw may bite in the act of mastication. It is exactly this epithelial layer, then, which becomes enormously developed in the whalebone whales to form the baleen-plates just described. That this is actually the case is ascertained by the development of the baleen-plates, as well as by their situation and relations to the gum and palate. And the recital becomes the more astonishing when we consider that, from cells of microscopic size in other animals, structures of enormous extent may be developed in the whales. The baleen-plates possess a highly important office. They constitute a kind of huge strainer or sieve, the possession of which enables the whale to obtain its food in a convenient fashion. Whether or not Biblical scholars and commentators agree in regarding the "great fish" which wrought calamity to the prophet Jonah as a special creation, and as an entirely different animal from the whale of to-day, the plain fact remains that a whale has a gullet of relatively small size when compared with the bulk of the animal. Fortunately, however, the faith of rational mankind is not pinned to literal interpretation of the untoward incident chronicled in Jonah, and, whale or no whale, it is curious to learn that the largest of animals may in a manner be said to feed on some of the most diminutive of its fellows. In the far north, and in the surface-waters of the Arctic seas, myriads of minute organisms, closely allied to our whelks, and like mollusks, are found. Such are the "Sea-butterflies," or Pteropoda of the naturalist: little delicate creatures which paddle their way through the yielding waters by aid of the wing-like appendages springing from the sides of the head and neck. These organisms are drawn into the mouth of the Greenland whale in veritable shoals, and as the