Let us sit down by this brook and look into it.
It is such a clear little stream, with fine sand and little pebbles at the bottom.
What has Nell found that pleases her so?
She says she sees some little bars of sand moving about.
Ned says they are not sand bars but tubes of sand, containing a little live thing.
The truth is, this sand bag is a house, and its occupant is a larva.
See the black head come popping out, and the tiny fore legs.
The larva does not come entirely out, you see, but pulls its house along with it, and when it is frightened it pops back into its little stone case.