256 THE ENZYME TREATMENT OF CANCER
of the chick, how from an apparently undifferentiated mass—what we should now term the “cleavage products”
—part was gradually added to part, very much in the same way that one may any day witness the building of a house from a heap of material—bricks, boards, beams, windows, and what not—lying upon the ground beside the site. Study the developmental history of an earthworm or leech, the whole development of a skate or mammal, and the possibility of epigenesis may appear in another light. But whether epigenesis be possible or not, nothing is more certain than that by no modern observer has it ever been proved to be the mode of origin of an embryo underlying the development. Incidentally, be it added, the foregoing passage and the doctrine of epigenesis itself show how great is the importance of “the embryo” in the embryological mind, and how little weight is really laid upon other phenomena of the life-cycle prior to its appearance.
The foundation-stones of epigenesis are direct development and a somatic origin of germ-cells. If these be removed, the whole structure of epigenesis will crumble away. Of the three tenets previously mentioned, possibly to none do embryologists cling with greater tenacity than to direct development. In the higher animals it is looked upon as the rule; indirect development is, indeed, recognized under the term “metamorphosis,” though doubtless no advocate of direct development has ever formed, or been able to formulate, any clear, logical conception, free from metaphysics and “Naturphilosophie,” of what he understands by “metamorphosis.” The term “metamorphosis” is not originally a scientific one at all. It belongs to the realm of the supernatural, and it has been imported into science—from mythology !—to account for facts, which at best it scarcely succeeds in explaining away. To take an instance, the trochophore larva of an annelid worm is said to become “metamorphosed” into the annelid. Were this ever really to happen, the phenomenon would be exactly comparable to that which in