195 HYPOTHESIS OF THE DEVELOPMENT OF THE VEGETABLE AND ANIMAL KINGDOMS. It has been already intimated, as a general fact, that there is an obvious gradation amongst the families of both the vegetable and animal king doms, from the simple lichen and animalcule re spectively up to the highest order of dicotyledonous trees and mammalia. Confining our attention, on this occasion, to the animal kingdom—it is to be observed that the gradation is much less simple and direct than is generally supposed. It certainly does not proceed, at all parts of its course at least, upon one line; for the two sub-kingdoms of middle rank, mollusca and articulata, form unquestionably two distinct approaches to the highest, the verte- brata. It even appears that there are intimations of more than two lines at various parts of the ani- k 2
