The pearls are generally found embedded in the flesh of the mollusk; quite often they are in a sac or cyst with an external opening form which they are sometimes dislodged by the muscular movement of the animal. The yield is small, a thousand shells in many cases yielding only a very small number of seed-pearls or perhaps none at all. Most of them are oval, commonly somewhat elongated. The usual size is about one grain in weight, but some of them weigh over twenty, and a very few exceed fifty grains each.
