Page:Popular Science Monthly Volume 17.djvu/490

474 nature. On close examination, the saucer-shaped partitions were proved to be all perforated at one point, and, the perforations being situated exactly in the same line, the chambers were seen to be traversed by a canal or siphuncle, which thus connected the smallest or apical chamber with the largest. There is nothing like this in the vegetable world; but an exactly corresponding structure is met with in the shells of two kinds of existing animals, the pearly Nautilus and the Spirula, and only in them. These animals belong to the same division—the Cephalopoda—as the cuttle-fish, the squid, and the octopus. But they are the only existing members of the group which possess chambered, siphunculated shells; and it is utterly impossible to trace any physiological connection between the very peculiar structural characters of a cephalopod and the presence of a chambered shell. In fact, the squid has, instead of any such shell, a horny "pen," the cuttle-fish has the so-called "cuttle-bone," and the octopus has no shell at all, or a mere rudiment of one.

Nevertheless, seeing that there is nothing in nature at all like the chambered shell of the Belemnite, except the shells of the Nautilus and of the Spirula, it was legitimate to prophesy that the animal from which the fossil proceeded must have belonged to the group of the ''Cephalopoda. Nautilus and Spirula'' are both very rare animals, but the progress of investigation brought to light the singular fact that, though each has the characteristic cephalopodous organization, it is very different from the other. The shell of Nautilus is external, that of Spirula internal; Nautilus has four gills, Spirula two; Nautilus has multitudinous tentacles, Spirula has only ten arms beset with horny rimmed suckers; Spirula, like the squids and cuttle-fishes, which it closely resembles, has a bag of ink which it squirts out to cover its retreat when alarmed; Nautilus has none.

No amount of physiological reasoning could enable any one to say whether the animal which fabricated the Belemnite was more like Nautilus, or more like Spirula. But the accidental discovery of Belemnites in due connection with black elongated masses which were certainly fossilized ink-bags, inasmuch as the ink could be ground up and used for painting as well as if it were recent sepia, settled the question; and it became perfectly safe to prophesy that the creature which fabricated the Belemnite was a two-gilled cephalopod with suckers on its arms, and with all the other essential features of our living squids, cuttle-fishes, and Spirulæ. The paleontologist was, by this time, able to speak as confidently about the animal of the Belemnite as Zadig was respecting the queen's spaniel. He could give a very fair description of its external appearance, and even enter pretty fully into the details of its internal organization, and yet could declare that neither he, nor any one else, had ever seen one. And, as the queen's spaniel was found, so happily has the animal of the Belemnite; a few exceptionally preserved specimens having been discovered which