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 organisation, 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 fossilised 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 palæontologist 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 organisation, 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 completely verify the retrospective prophecy of those who interpreted the facts of the case by due application of the method of Zadig.