"So those who first discovered these great bones, having reconstructed the animals whose skeletons they formed, gave them scientific names best fitted to describe them. Can you think of anything more aptly descriptive than 'thunder-lizard,' to indicate a beast shaped like the lizards we see to-day, and yet whose size would terrify ancient man as thunder terrified him?" The boys were really enjoying this scientific information, dry and complicated as it must seem in the way I have written it down here. But the professor had a way of making the most dry and scientific subject seem interesting. "What gets me, though," said Dick, "is how they know about how these big lizards and other things look when they only find a single bone, or maybe one or two." "That is puzzling at first," admitted Professor Wright. "Perhaps I can illustrate it for you. Take, for instance, the Dinornis--and before we go any farther let me see if you can give me a good English name for the creature. Try it now--the Dinornis." He looked expectantly at the boys. "Dino--dino--" murmured Bud. "That must mean--why that must mean fierce or terrible, if it's anything like Dinosaur." "I'll encourage you so far as to say you're on the right track. In other words, you are half right," said the scientist. "Suppose you take a try at it," and he turned to Dick. "There isn't much left," laughed the lad. "Suppose you take it this way," suggested the scientist. "Lop off just di--and assume that Bud has used that. You have left the syllable nornis." "Nornis--nornis--it doesn't seem to mean anything to me," sighed Dick, for he was rather disappointed at Bud's success and his own seeming failure so far. "I'll help you a little," offered the professor. "Instead of saying di-nornis, call it din-ornis. Did you ever hear the word _ornithology_?" "Sure!" assented Bud. "It means--_ology_ that's the science of," he was murmuring to himself. "Don't tell me now--I have it--the science or study of birds. That's what ornithology is--the study of birds." "Correct," said the professor. "Ornis is the Greek word for bird, and when we put in front of it Di, or din, meaning fear, thunder or terror, we have a word meaning a terribly large bird, and that's just what the Dinornis is--an extinct bird of great size. "But what I started to tell you was how we can sometimes--not always and sometimes not correctly--reconstruct from a single bone the animal that once carried it around with it. The Dinornis is a good example. "Some years ago there was discovered the pelvic and leg bones of what was evidently an enormous extinct bird. Now, of course, our knowledge of the past is based somewhat on our knowledge of the present, and if we had but the pelvic and leg bones of, say, a crow, we could, even without ever seeing a crow, come pretty nearly drawing the picture of how large a bird it is, and of what shape to be able to use such a pelvis and such leg bones.