When you put it with the hinge on the top, and have a close look at it, you will find it has a flat valve and a round valve.
If you remove the round valve,you will see what the illustration on the right shows.
The mantle connected to the shell plays an essential role in forming a pearl.
This organ has the important function of forming the shell as well as controlling the quantity of water which the oyster absorbs to take in oxygen and food.
The shell consists of a "periostracum,"a "prismatic layer," and a "nacreous layer."
The iridescent nacreous layer is formed by the outer epithelium of the mantle.
The internal organs lie in the milky white part, most of which is occupied by the digestive system,from the mouth to the vent;and the gonads.
In order to cultivate a pearl, a small incision is made in the internal organ part and a piece of mantle tissue and a core are inserted into the gonads through the incision.
