Baron Cuvier, one of the most famous of the paleontologists, awoke from a deep sleep to see standing by his bed a strange, hairy creature with horns and hoofs. And it said:
"Cuvier! Cuvier! I have come to eat you!" But the baron, taking in the form of the monster at a glance, only laughed.
"Horns and hoofs? You can't. You're a grain-eater!"
See the point? The baron argued that because the monster had horns and hoofs he must be a grain-eater; for all creatures with both horns and hoofs are grain-eaters. This particular creature, to be sure, was an eater of both meat and grain--being one of Cuvier's students who was trying to play a trick on him. But the principle holds good. The scientists, _knowing_ one thing, _infer_ another. Because animals with both horns and hoofs eat no meat Cuvier knew his visitor couldn't eat _him_, even if he'd been real and not just made up.
For another instance, take our queer old friend that Professor Blackie wrote the funny rhyme about--the Ichthyosaurus "with a saw for a jaw and a big staring eye." The scientists figure, just from looking into the hollow socket where the eye used to be, that he could see at night like a cat--and right through muddy water, too; that he spent most of his time in shallows near the shore; that it didn't make any difference to him whether a fish was near or far, provided it wasn't too far, of course, for he could see it and catch it, just the same. They also said--these learned men, after peering into the dark hollow where that remarkable eye used to be--that Mr. Ichthyosaurus spent a great deal of time diving and a great deal of time with his homely face just above the surface of the water.
Why they could reason all this from a hollow eye socket and some bony, flexible plates around the outer edge of it, you will see by referring to such books as "Animals of the Past," by F. A. Lucas, director of the American Museum of Natural History; "Creatures of Other Days" and "Extinct Monsters," by Hutchinson; "Extinct Animals," by Lankester; "Mighty Animals," by Mix; the chapter "When the World was Young," in Lang's "Red Book of Animal Stories," and "Restoring Prehistoric Monsters" in "Uncle Sam, Wonder Worker," by Du Puy.