"But the head of a sperm whale is almost square; and no other fish is like him," added Phil Gawner.
"The whale is not a fish, Gawner. I have seen a school of porpoises alongside an ocean steamer. Their greatest girt is one third of the length from the head end; but they will swim past a fast steamer, and make something like twenty knots an hour," said Captain Gildrock.
"I was trying to find the porpoise in Wood's Natural History the other day; but there is no such fish in the book," added Sol Guilford.
"Where did you look?"
"In the volume about fishes."
"The porpoise is not a fish, and you would have found it in the volume marked 'Mammalia,'" replied the principal with a smile.
"But isn't the porpoise a fish? He lives in the water."
"So do hippopotami; but they are not fishes. Whales, porpoises, dolphins, seals, and some others, are mammals; that is, they suckle their young as a cow does a calf. Properly they are not fishes, though they are very often called so."
These were the kind of questions the captain believed in encouraging, though they sometimes led the conversation out of the legitimate channel. They elicited useful information; and he was careful not to let the students wander too wide of the subject under discussion.