It is well - known that certain types of oysters can turn irritants small fragments of stone, for instance into lustrous pearls by enveloping them in layers of a secretion known as nacre.
ক্ৰমান্বয়ে তেনে প্ৰক্ৰিয়াৰ ফলত সেই বালিৰ কণা বা শিল টুকুৰা মুকুতালৈ পৰিণত হয় ।