Let us now see for ourselves, in this spirit, whether there may not be something absolutely derogatory, in the existence of a cartilaginous skeleton, to the creatures possessing it; or whether a deficit of internal bone may not be greatly more than neutralized, as it assuredly must have been in the view of Linnæus, Muller, and Owen, by a larger than ordinary share of a vastly more important substance. THE PLACOID BRAIN. EMBRYONIC CHARACTERISTICS NOT NECESSARILY OF A LOW ORDER. That special substance, according to whose mass and degree of development all the creatures of this world take rank in the scale of creation, is not _bone_, but _brain_. Were animals to be ranged according to the solidity of their bones, the class of birds would be assigned the first place; the family of the _Felidæ_, including the tiger and lion, the second; and the other terrestrial carnivora the third. Man and the herbivorous animals, though tolerably low in the scale, would be in advance of at least the reptiles. Most of these, however, would take precedence of the sagacious _Delphinidæ_; the osseous fishes would come next in order; the true Placoids would follow, succeeded by the _Sturiones_; and the _Suctorii_, _i. e._ Cyclostomi or Lampreys, would bring up the rear. There would be evidently no order here: the utter confusion of such an arrangement, like that of the bits of a dissected map flung carelessly out of its box by a child, would of itself demonstrate the inadequacy and erroneousness of the regulating principle. But how very different the appearance presented, when for _solidity of bone_ we substitute _development of brain_! Man takes his proper place at the head of creation; the lower mammalia follow,—each species in due order, according to its modicum of intelligence; the birds succeed the mammalia; the reptiles succeed the birds; the fishes succeed the reptiles; next in the long procession come the invertebrate animals; and these, too, take rank, if not according to their development of brain proper, at least according to their development of the _substance_ of brain. The occipital nervous ganglion of the scorpion greatly exceeds in size that of the earthworm; and the occipital nervous ring of the lobster, that of the intestinal Ascaris. At length, when we reach the lowest or _acrite_ division of the animal kingdom, the substance of brain altogether disappears. It has been calculated by naturalists, that in the vertebrata, the brain in the class of fishes bears an average proportion to the spinal cord of about two to one; in the class of reptiles, of about two and a half to one; in the class of birds, of about three to one; in the class of mammals, of about four to one; and in the high-placed, sceptre-bearing human family, a proportion of not less than _twenty-three_ to one. It is palpably according to development of brain, not development of bone, that we are to determine points of precedence