boundary line, so as to say that all the organisms on the one side of the line are assuredly animals, while all the others on the opposite side of the line may be declared to be truly plants.  It is exactly this task which science declares to be among the impossibilities of knowledge.  Away down in the depths of existence and among the groundlings of life the identity of living things becomes of a nature which is worse than confusing, and which renders it a futile task to attempt to separate the two worlds of life.  The hopelessness of the task, indeed, has struck some observers so forcibly that they have proposed to constitute a third kingdom—­the Regnum Protisticum—­between the animal and the plant worlds, for the reception of the host of doubtful organisms.  This third kingdom would resemble the casual ward of a workhouse, in that it would receive the waifs and strays of life which could not find a refuge anywhere else.

A very slight incursion into biological fields may serve to show forth the difficulties of naturalists when the task of separating animals from plants is mooted for discussion.  To begin with, if we suppose our popular disbeliever to assert that animals and plants are always to be distinguished by shape and form, it is easy enough to show him that here, as elsewhere, appearances are deceptive.  What are we to say of a sponge, or a sea anemone, of corals, of zoophytes growing rooted from oyster shells, of sea squirts, and of sea mats?  These, each and all of them, are true animals, but they are so plant-like that, as a matter of fact, they are often mistaken by seaside visitors for plants.  This last remark holds especially true of the zoophytes and the sea mats.  Then, on the other hand, we can point to hundreds of lower plants, from the yeast plant onward, which show none of the ordinary features of plant life at all.  They possess neither roots, stems, branches, leaves, nor flowers, so that on this first count of the indictment the naturalist gains the day.

Power of movement, to which the popular doubter is certain to appeal, is an equally baseless ground of separation.  For all the animals I have above named are rooted and fixed, while many true plants of lower grade are never rooted at all.  The yeast plant, the Algae that swarm in our ponds, and the diatoms that crowd the waters, exemplify plants that are as free as animals; and many of them, besides, in their young state especially (e.g., the seaweeds), swim about freely in the water as if they were roving animalcules.  On the second count, also, science gains the day; power of motion is no legitimate ground at all for distinguishing one living being as an animal, while absence of movement is similarly no reason for assuming that the fixed organism must of necessity be a plant.  Then comes the microscopic evidence.  What can this wonder glass do in the way of drawing boundary lines betwixt the living worlds?  The reply again is disappointing to the doubter; for the