the Pearl Oijster and on the Production of Pearls, 99 



portion of pearl-bearing individuals among them. This, of 

 course, requires more extensive practical observation, either on 

 the beds in the harbour of Trincomalie, or on the pearl-banks 

 of Arripo." 



Under any circumstances, this retraction and extrusion of the 

 mantle must be of considerable importance in determining the 

 internal structure of the pearls ; for as the different layers of the 

 shell (epidermis, columnar layer, and nacre) are secreted by dif- 

 ferent parts of the surface of the mantle, the pearls which con- 

 tain more than one of these substances must have been in contact 

 successively with the corresponding regions of the mantle. Thus 

 if a pearl be originally formed at the edge of the mantle (which 

 will be the case when dead extraneous matters get within the' 

 shell, w^hilst the mantle is retracted as above described), the 

 nucleus will be immediately surrounded by a layer of epidermis ; 

 and if it be subsequently passed inwards (by the extrusion of the 

 mantle or otherwise) through the columnar region to that which 

 secretes the nacreous layer, it will exhibit the three layers in the 

 same order as in the shell. The finest pearls are those formed 

 entirely in the nacre-secreting portion of the mantle ; but if 

 those originally produced in this situation be passed outwards 

 (by the retraction of the mantle or otherwise), they will acquire 

 a columnar, and even an epidermic, layer; and by passing 

 inwards again, these may be in their turn coated with nacre. 

 Instances of the structures thus produced appear not to be 

 uncommon, and several of them are described and figured by 

 Dr. Mobius. Pearls found imbedded in the tissues of the body 

 at a distance from the mantle, are probably carried to their 

 resting-place by the circulation. 



Ever since the admission of the fact that the formation of 

 pearls is caused by the intrusion of foreign bodies between the 

 mantle of the moUusks and their shell, attempts have been made 

 to produce similar effects by artificial means. In 1761 Linnaeus 

 announced to the King and Diet of Sweden that he could com- 

 pel mollusks to produce pearls, at the same time offering to 

 publish his method for the benefit of the State. He seems, how- 

 ever, to have thought better of the matter, and sold his secret 

 for 500 ducats to one Bagge, a merchant of Gothenburg, whose 

 heirs offered it for sale again in 1780. Beckmann, who narrates 

 this, says : "Linne once showed me in his collection a tray of 

 pearls, and said, ' Hos unionis confeci artificio meo ; sunt tan- 

 tum quinque annorum, et tamen tarn magni.'^' Beckmann 

 adds, — " I believe that Linne had described his art as early as 

 1746 in one of his works, before he had the idea of making use 

 of it as a mystery. I refer to a line in the sixth edition of the 

 ' Systema Naturae,' at p. 1 95, which runs, — ' Margarita, testae 



7* 



