CHAP. XXI - Functions and Instincts. Fishes

Summary

The animals we have hitherto considered have been destitute of an internal jointed vertebral column and its bony appendages; and though some, as the Cephalopods and some slugs, have a kind of internal bone, and in one Order of Polypes the axis is sometimes articulated, yet these, especially in the latter instance, merely indicate an analogical relation, but no affinity. In none of these instances is this internal bone perforated for the passage of a spinal marrow, as in a real vertebrated column; we now, however, enter that superior section of the animal kingdom, the individuals belonging to which, with scarcely any exception, are built upon the column in question, incasing a spinal marrow, and terminated at its upper extremity by a bony casket, calculated to contain and protect the most precious and wonderful of all material substances, the cerebral pulp, by which the organs of sense perceive; the will moves the members; the mind governs the outward frame; and, in the king of animals, an immortal spirit, is enabled to seek and secure a higher destiny.

This change in the structure of animals was rendered necessary by an increase in their bulk, for though there are some of the invertebrated Sub-kingdom, as the fixed Polypes and several of the Cephalopods, that are of as large dimensions, and a few of the vertebrated, as the humming birds, and the harvest mouse, that are not so large as some insects; yet the generality of those distinguished by a vertebral column form a striking contrast, as to magnitude, with those that are not.