“Oh, how funny!” said Frank. “It is divided into two large things like horns.”
“These,” said his uncle, “are the hooks by which he fixes himself so firmly in his case.”
“And what are all these curious big bristles for?” asked Tom. “They are all over his body.”
“These are his breathing organs,” Uncle George answered. “The caterpillar, if you remember, had breathing-holes along the sides of his body. By moving his long body, the caddis worm causes a constant current of water to pass through his dwelling.
“Look at the fourth segment of his body. How does it differ from the others?”
“It is the broadest segment,” said Frank, “and there is a stout rounded thing in the middle of it.”
“Yes,” his uncle replied, “and if we can get him turned on his back we shall see two more of these stout outgrowths below, one on each side of the same segment. This is really very clever. By it the animal keeps himself in the middle, so that the current of water must flow all around him.
“Now, look at the case of a sleeping caddis.”
“The front of the case is closed,” said Frank.
“How is it closed, Frank?”