Now look at Mr. Whirligig's eyes, you see each is separated into two parts by a division; the one is on the upper part of the head and looks towards the sky, the other is on the under part of the head and looks into the water. Now let us all keep quite still--the whirligigs rest. Now let us move--just look, they see our motions and off they start on their merry-go-rounds. It was with this upper part of the eye they saw us; should some sly fish, from below the surface of the water, make a rush at one, the beetle sees the enemy with his under eye and avoids him. What have you caught now, Jack? fish him out whatever it is. Oh! a fresh-water mussel, and a very fine specimen too; there are plenty of these fellows in the canal all the way from here to Newport. "Are they good to eat, papa?" asked Willy. I never tried one, but, from having often dissected specimens, I should say they were as tough as the sole of a boot. I never heard of anyone eating them. These molluscs carry their eggs, myriads in number, within their gills. The young, at the time they are ejected, are very curious little animals with triangular shells, and, oddly enough, they will fasten upon the fins or tails of fish, on which they will stick for some time, but how long I do not know. [Illustration: FRY OF SWAN-MUSSEL, PARASITIC ON A FISH'S FIN.] [Illustration: FRY OF SWAN-MUSSEL, HIGHLY MAGNIFIED.] This particular mollusc is known by the name of swan-mussel; the young fry are sent into the water in April and May. There is another kind of fresh-water mussel in rivers and streams, called the pearl-mussel, pearls being occasionally found in them. I had one of these pearls once given me by a lad, taken from a river in the Isle of Man. I took it to a jeweller, in Liverpool, who valued it at a guinea. Your uncle Arthur, to whom I gave it, had it set in gold as a pin "I wish," said May, who had listened to this part of the story with great attention, "I wish pearl-mussels would live in the canal, it would be so nice to get the pearls out of them." Very few mussels are found to contain the pearls; perhaps you might have to open many hundreds before you found a single pearl, and I should not like to cause the death of so many harmless animals for the sake of a single pearl. [Illustration: FRESH-WATER MUSSEL.] "Here is another swan-mussel, and, just look, papa," said Jack, "some other shells are fastened on it." So there are; it is a lot of the curious and pretty little zebra-mussel. How prettily they are marked with zig-zag stripes of reddish brown, especially the young specimens. The name of mussel is better suited to these molluscs than to the large kinds upon which the "zebras" are often attached, because, like the salt water mussel you have often seen at New Brighton, they have the power of spinning, what is called, "a byssus"--here, you see, is the substance I mean--by which they fasten themselves to shells, or to stones, roots, and other things.