After the statical analysis of living bodies, there must be a hierarchical co-ordination of all known, or even possible organisms, in a single series, which must serve as a basis for the whole of biological speculations. The essential principles of this philosophical operation are what I have now to point out.

Comparative anatomy of vegetables and animals

We have already seen that it is the distinction of biological science to have developed the theory of classifications, which, existing in all sciences, attains its perfection when applied to the complex attributes of the animal organisms. In all ages, the vegetable organism was the direct subject of biological classification ; but it was pursued on the principles furnished by the consideration of animals, whence the type was derived which guided philosophical speculation in the case. It could not be otherwise, so marked and incontestable as are the distinctions among animal organisms: and even the zoological classification of Aristotle, imperfect as it is, is infinitely superior to anything which could then have been attempted with regard to vegetables. This natural original classification has been rather rectified than changed by the labours of modern times; while that of vegetables has met with an opposite fate.