Page:Popular Science Monthly Volume 27.djvu/215

Rh see in animal structures. Although appearing at first sight an entirely distinct and special formation, it evidently consists of nothing more than the highly modified papillæ of the lining membrane of the mouth, with an excessive and cornified epithelial development.

The bony palate of all mammals is covered with a closely-adhering layer of fibro-vascular tissue, the surface of which is protected by a coating of non-vascular epithelium, the former exactly corresponding to the derm or true skin, and the latter to the epiderm of the external surface of the body. Sometimes this membrane is perfectly smooth, but it is more often raised into ridges, which run in a direction transverse to the axis of the head, and are curved with the concavity backward; the-ridges, moreover, do not extend across the middle line, being interrupted by a median depression or raphé. Indications of these ridges are clearly seen in the human palate, but they attain their greatest development in the Ungulata.

Though the early stages by which whalebone has been modified from more simple palate structures are lost to our sight, the conditions in which it now exists in different species of whales show very marked varieties of progress, from a simple, comparatively rudimental and imperfect condition, to what is perhaps the most wonderful example of mechanical adaptation to purpose known in any organic structure.

In the rorquals or fin-whales (genus Balænoptera), found in almost ail seas, the largest blades in an animal of seventy feet in length do not exceed two feet in length, including their hairy terminations; they are in most species of a pale horn color, and their structure is coarse and inelastic, separating into thick, stiff fibers, so that they are of no value for the ordinary purposes to which whalebone is applied in the arts. These animals feed on fish of considerable size, from herrings up to cod, and for foraging among shoals of these creatures the construction of their mouth and the structure of their baleen are evidently sufficient. This is the type of the earliest known extinct forms of whales, and it has continued to exist, with several slight modifications, to this day, because it has fulfilled one purpose in the economy of Nature. Other purposes for which it was not sufficient have been supplied by gradual changes taking place, some of the stages of which are seen in the intermediate conditions still exhibited in the Megaptera and the Atlantic and southern right whales.

In the Greenland right whale of the circumpolar seas, the Bowhead of the American whalers (Balæna mysticetus), all the peculiarities which distinguish the head and mouth of the whales from other mammals have attained their greatest development. The head is of enormous size, exceeding one third of the whole length of the creature. The cavity of the mouth is actually larger than that of the body, thorax, and abdomen together. The upper jaw is very narrow, but greatly arched from before backward, to increase the height of the cavity and allow for the great length of the baleen; the enormous rami