“You see there are comparatively few species of fish that have any teeth at all. They have no need of teeth and therefore have never developed them.”
“But why is that,” asked Tom; “I should think some of the toothless varieties of fish would have developed teeth accidentally, as it were.”
“Development is never accidental in that sense, Tom. It is Nature’s uniform law that every species of living thing, animal or vegetable, shall tend to develop whatever is useful to it, and nothing else. That is Nature’s plan for the perpetuation of life and the improvement of species.”
After pausing in close attention to some detail of his work, Dunbar went on:
“You can see the same dominant principle at work in the varying forms of teeth developed by different species. The sheepshead needs teeth only for the purpose of crushing the shells of barnacles and the like, and in that way getting at its food. So in a sheepshead’s mouth you find none but crushing teeth. The shark, as you see, has pointed teeth so arranged in rows that one row closes down between two other rows in the opposite jaw, and by a muscular arrangement the shark can work one jaw to right and left with lightning-like rapidity, making the saw-like row of teeth cut through almost anything after the manner of a reaping machine. Then there is the pike. He has teeth altogether different from either of the others. The pike swallows very large fish in proportion to his own size, and his need is of teeth that will prevent his prey from wriggling out of his mouth and escaping while he is slowly trying to swallow it. Accordingly his teeth are as small and as sharp as cambric needles. Moreover, he has them everywhere in his mouth—on his lips, on his tongue, and even in his throat. However, this is no time for a lecture. If you are interested in the subject you can study it better by looking into fishes’ mouths than by listening to anybody talk or by reading books on the subject.”
Again Dunbar paused in order that his attention might be closely concentrated upon some delicate detail of his work.
When the strain upon his attention seemed at last to relax, Cal ventured to say something—and it was startling to his comrades.
“Of course you’re right about the books on such subjects,” he said. “For example, the most interesting of all facts about fish isn’t so much as mentioned in any book I can find, though I’ve searched through several libraries for it.”
“What is your fact?” asked Dunbar, suspending his work to listen.
“Why that fish do not die natural deaths. Not one of them in a million ever does that.”