Part 20

“Because he has a soft body.”

“Quite right. But why is he forced to protect his body?”

“Fishes would eat him.”

“Right again, Frank. If trout could speak, they might tell you that the sweetest morsel in the stream is the caddis worm. Now, take your lens, please, and tell me something about him.”

“His body is divided into rings, and there are the same number of them as we found in the caterpillar.”

“Very good, Frank. Now give Tom a chance.”

“His head and the first three divisions of his body are hard cased. They are black and yellow in colour.”

“He has six legs,” said Frank, “and they are attached to the first three divisions of his body.”

“What about the last division of his body?” Uncle George asked.

“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?”

“Well, there is a network of threads over it,” answered Frank.

“Yes; you see a caddis worm cannot do without fresh water, even when he is asleep; so, before going to sleep, he builds a grating over the entrance.

“When he wakes up, he has quite a new shape altogether. And this brings us to those things which Tom said were like ‘earwigs.’ There are five of them floating on the water, and two of these are dead. If you look, you will find five empty caddis cases in the tank.”

“How does he get out of the case?” inquired Tom.

“Easily enough. Look at the strong pair of pincers he has got for cutting his way through the silken grating with. No longer burdened with his heavy case, he floats up to the surface. He crawls up out of the water into the air.

“If there are no rushes or floating leaves about, he is sure to drown; for your caddis is no longer a water insect, but a fly inside a thin skin.

“Now, boys, I am going to show you something wonderful.”

Uncle George then took out the three living pupæ that were floating on the water, and placed them on the table. The boys watched them for a long time.

They were beginning to get impatient, when suddenly the skin of one of the creatures burst along the back, and a lovely little fly, with brown, gauzy wings and long feelers, came out.