, as having been metamorphosed, not one from the other, as they now exist, but from some common and simpler element.

Most naturalists, however, use such language only in a metaphorical sense: they are far from meaning that during a long course of descent, primordial organs of any kind--vertebrae in the one case and legs in the other--have actually been converted into skulls or jaws.

Yet so strong is the appearance of this having occurred that naturalists can hardly avoid employing language having this plain signification.