“Mammals,” said Delia’s father.
“Now let’s restate our data, still ignoring the first warning, of which none of us had firsthand knowledge but Mr. Priam. The second warning was fish. The third warning was amphibians. The fourth warning was reptiles. The fifth warning was birds. The sixth warning was mammals.
“Immediately we perceive a change in the appearance of the warnings. From being an apparently unrelated, rather silly conglomeration, they’ve taken on a related, scientific character.
“Is there a science in which fish, amphibians, reptiles, birds, and mammals are related ― what’s more, in exactly that order?
“In fact, is there a science in which fish are regarded as coming ― as it were ― second, amphibians third, reptiles fourth, birds fifth, and mammals last? ― exactly as the warnings came?
“Any high school biology student could answer the question without straining himself.
“They are progressive stages in the evolution of man.” Roger Priam was blinking steadily, as if there were a growing, rather too bright light.
“So you see, Mr. Priam,” said Ellery with a smile, “there was no bluff involved whatever. Since the second warning, fish, represents the second stage in the evolution of man, and the third warning, amphibians, represents the third stage in the evolution of man, and so on, then plainly the first warning could only have represented the first stage in the evolution of man. It’s the lowest class of what zoologists call, I believe, craniate vertebrates ― the lamprey, which resembles an eel but belongs to a different order. So I knew, Mr. Priam, that when you opened that first box you found in it something that looked like an eel. There was no other possibility.”
“I thought it was a dead eel,” said Priam rigidly.
“And did you know what the thing that looked like a dead eel meant, Mr. Priam?”