idly. Even a
small fish, four inches in length, can carry five hundred of these
little creatures on its fins and in its gills without serious injury."

"Suppose it can't find a fish?"

"That's the end of the mussel, then! There is one kind of mussel that
develops without going through the parasite stage, but it is not as
common as the others. Curiously enough, the only way to raise the mussel
artificially is by means of parasitism on the fish. As you read there,
it is a simple matter to get these tiny creatures from the 'pouch' of
the mother mussel, put them in an aquarium with some fish, and keep the
water stirred up. In a few minutes the larvae will have fastened
themselves on. It is wise to keep these fish in a hatchery for a month
or so and then simply release them; when the mussels are ready they will
drop off, and a new crop of mussels is on the way. By this means you can
start them without much trouble in rivers and streams where there were
none before, so that you see what chances there are for the development
of the industry."

"Are all mussels equally good for making mother-of-pearl?"

"No," was the reply. "There are two chief commercial varieties, of
different species, one larva having a hook on the shell, so that it can
attach to fins or tail, the other being smaller and without hooks and
making its way into the gills. But you'll go into all that when you get
to Fairport, and even after you have worked at mussels all summer there
will be a lot of problems you won't have touched. Don't forget now, the
fifteenth."

"Never fear, Dr. Crafts," Colin answered; "I won't forget. I wish it
were here now."

Time did not hang heavily on the boy's hands, for he was interested in
all phases of fishing, and spent a couple of weeks on a trout stream in
Northern Maine, not only catching the fish, but--as he had been
advised--making notes of any peculiarities he saw in those he caught.
Many stories had been told him of the finding of new species by young
investigators, and he was amazed to see what wide differences existed in
fish of the same species.

Colin examined so carefully every one he caught, that he began to think
that if the fish were thrown back into the stream and hooked out again,
he could recognize each one of them. His eagerness to be at work reached
boiling point when a newspaper arrived at the camp with a brief item
telling of the excitement caused by the finding of pearls near Fairport.
Fortunately