Page:Popular Science Monthly Volume 82.djvu/551

Rh some months beautiful pearls were secreted, their size being in proportion to the length of time of the culture.

In our red abalone a boring mollusk, Pholadidea, penetrates the shell from the outside. It files its way, by means of sharp teeth on its shell and possibly by the secretion of sulphuric acid. The burrow enlarges, as the Pholadidea, growing in size, digs its way in. When near the inner pearly layer of the abalone shell, the host resists the oncoming Pholadidea by secreting more nacreous matter. Thus the defensive wall, eaten by the Pholadidea, grows inwardly as a mound shaped projection, the blister-pearl. In imitation of this natural process, a hole is drilled through the abalone shell and a form is inserted. This form, made of shell, is shaped like a long-shanked collar button and so placed that the expanded curved base lies against the pearl-secreting mantle. The shank projects from the outer surface of the abalone shell and is there made fast by aluminum wire, to which a metal tag, bearing the serial number, is attached. In some cases the wire has corroded, with the loss of the tag. In later experiments the numbers have been filed upon the shell. The black abalone has been used in most cases, although a few experiments have been made upon the green abalone. Holes have been drilled through various parts of the shell and different numbers of forms inserted. In addition, spherical forms, without shanks, have been placed beyond the mantle cavity near the visceral hump. I have succeeded in raising abalone culture