If we employ the twofold method of classification recommended in the preceding part of this work, we shall be at no loss to obtain the first divisions of the animal kingdom, vertebral and invertebral, however great difficulty may be experienced in the construction of the subordinate groups. These two divisions depend, the one on a positive, the other on the negative character, and possess the advantage of being easily recognized. In this respect, and indeed in every other, they have the decided superiority. Any other basis of division hitherto employed is faulty, in not including a number of common properties, in effecting unnatural separation among kindred tribes, or in being founded on characters which are merely modifications of some positive quality. Without wasting the time of the reader, in dwelling on the defects of these different systems, we shall proceed at once to an exposition of the characters of the method employed.
CHARACTER.—ANIMALS FURNISHED WITH A SKULL AND VERTEBRAL COLUMN FOR THE PROTECTION OF BRAIN AND SPINAL MARROW.
Description.—The properties which the vertebral aniitials possess in common, are numerous, and clearly indicate the unity of the plan according to which they have been constructed. In reference to the nervous system, indeed, a conformity of character here prevails, which is not observable in that, or any other system of organs among the invertebral tribes.