Histological Observation on Pearl-Sac Formation of the Pearl-Oyster, Pinctada martensii (DÜNKER)―II Especially, on Pearl-Sac Formation after an Artificial Injury had been given to the Inner or Outer Epidermal Cells of the Cut Piece from the Mantle (Piece)

For two months from August to September, 1955, on the coast of Sakibe, Sasebo Bay, Nagasaki Prefecture, we observed histologically the effect on the pearl-sac formation after the operation had been done to the inner and outer epidermis of the mantle piece of the pearl-oyster (Pinctada martensii), giving an artificial injury of applying 5% solution of AgNO3 for 1, 3, 5 and 10 minutes. The results obtained are as follows:- 1. When we observe the relation between the time and stage required for the injury done with 5% AgNO₃, we find that it takes the inner and outer epidermal cells of the piece about 10 minutes to have almost perfect injury, but as the surface of the mantle piece is uneven it is quite difficult to give perfectly even injury to the outer surface. 2. After we have done an operation giving an injury to the outer epidermal cells of the mantle piece, we find that these cells will grow to be high columnar pearl-sac outer ones recovering from the injury and increasing themselves greatly in number. The outer epidermal cells on the surface of the mantle piece will be the highest from the period of the secretion of periostracal substance to the early period of prismatic substance. After these periods are over, they will gradually decrease in height and become low and flat, but if they are severely injured, you can see, within 2 or 4 days after this, the formation of the outer epidermal cells of the mantle piece even on the surface of the muscle bundle of the mantle piece. 3. The more we give injury to the inner and outer cells of the mantle piece, especially when severer injury is given to the latter, the slower the pearl-sac formation will become and the weaker the secrtory activity, especially nacreous secretion. The crystal of secretion has the tendency to form uneven granular layer: the kind or the quantity of the secretion will also have the tendency to be irregular in the different parts of the same one pearl sac. To sum up, it can be said that the above mentioned tendencies will likely be the cause of forming baroque pearls