If we pass up into the kingdoms of the living, and study plants and animals, the same unity of phenomena meets us. Our classification terms--order, genus, species, and so forth--are as artificial as our names for the geological systems. No one holds to-day that any single species is clearly marked off from all others. Connecting links abound in our vegetable kingdom. The lichens, long regarded as a separate class of lowly organised plants are now known to be fungi that are parasitic upon algae. The higher cryptogams or flowerless plants are found to be at one in their structure and functions with the lower phsenogams or flowering plants. The distinctions between plants and animals are found to have vanished. Once again it is easy enough to distinguish high plants from high animals. But no man can satisfactorily draw the line between the lower members of the two kingdoms. The old definitions of the animal and the plant given with a suicidal glibness in old books on botany and zoology, when tried in the balance of criticism, are found wanting. Even the food-distinction, supposed to be the best distinction between the two groups, fails. It is no longer true that plants feed on the inorganic, and animals on organic substances. The cases of vegetable parasites and of insectivorous plants give a direct contradiction to this statement. And it is very interesting to notice how gradual are the transitions in this as in all cases. A group of plants known as saprophytes, that feed on decaying organic things, is the natural transition between the ordinary plants that eat inorganic food-stuffs, and those plants that, like animals, exist on organic substances. So marked is this difficulty of distinguishing between the lower plants and the lower animals, that it has been suggested that a third kingdom of the living should be constructed midway between the two generally recognised. This is to be called Protista, and is to include all the doubtful forms that are not clearly members either of the Kingdom Animalia or of the Kingdom Vegetabilia. If the arbitrary nature of all our systems of classification is understood, this new division will do little harm. But for the systematist the difficulty is by the establishment of this group only doubled. Heretofore he had only to struggle over a particular living, thing, with the view to determine whether it were plant or animal. Now he will have to struggle over it with the view of telling whether it is Protistic or animal, or Protistic or vegetable. But the true evolutionist will only look on the group of the Protista as containing forms that represent the parent condition of both vegetables and animals.