“No, Uncle George, I don’t,” he said. “Until this minute I never stopped to think that an elephant’s tusks were teeth.”
“What did you think they were? Horns?”
“I—I hadn’t ever thought,” stammered Perry, confused. “I just thought of them as tusks.”
“They are the incisors,” the scientist replied. “Now, in Moeritherium, you can see that the second incisors are developed both in the upper and lower jaws.”
He held out the skull to the boy.
“Yes,” Perry answered, “that’s easy enough to see.”
“Now in the skull of Paleo-mastodon, as I explained to you fully last night, there were rudimentary first incisor teeth. You remember that?”
“Yes,” answered the boy.
“And the elephant hasn’t any first incisors at all.”
“Oh!” exclaimed Perry, “I’m beginning to get hold of the idea. The Moeritherium shows how the tusks started.”