We have seen that some of the Silurian placoids were large of size; the question still remains, Were they high in intelligence and organization?

The Edinburgh Reviewer, in contending with the author of the “Vestiges,” replies in the affirmative, by claiming for them the first place among fishes. “Taking into account,” he says, “the brain and the whole nervous, circulating, and generative systems, they stand at the highest point of a natural ascending scale.” They are fishes, he again remarks, that rank among “the very highest types of their class.”

“The fishes of this early age, and of all other ages previous to the Chalk,” says his antagonist, in reply, “are, for the most part, cartilaginous. The cartilaginous fishes,—Chondropterygii of Cuvier,—are placed by that naturalist as a second series in his descending scale; being, however, he says, ‘in some measure parallel to the first.’ How far this is different from their being the highest types of the fish class, need not be largely insisted upon. Linnæus, again, was so impressed by the low characters of many of this order, that he actually ranked them with worms. Some of the cartilaginous fishes, nevertheless, have certain peculiar features of organization, chiefly connected with re-production, in which they excel other fish; but such features are partly partaken of by families in inferior sub-kingdoms, showing that they cannot truly be regarded as marks of grade in their own class.