332 DR. H. LYSTER JAMESON ON 



solitary pearl, which before calcification measured somewhat over 

 a millimetre in diameter, but when decalcified shrunk to "7 mm. 

 It was situated in the left side, in the wall of the visceral mass, 

 over the stomach. In section (PI. XLI. fig. 33) the pearl is seen 

 to lie in the subepidermal parenchyma (par.), projecting a little 

 through the muscular coat (^nusc.) into the visceral connective- 

 tissue {c.t.), in which the tubules of the ovary (ov.) and muscular 

 strands to the wall of the stomach (^musc.') are seen. The pearl- 

 sac has been ruptured, presumably by the evolution of bubbles of 

 carbon dioxide during decalcification. 



The pseudo-nucleus, which measures about ■3 mm. in diameter, 

 consists of several layers of columnar substance (col.) formed 

 around a small central cavity. Probably such a pearl would, as 

 it increased in size, grow through the muscular layer and 

 work its way into tlie visceral mass ; indeed, as soon as more 

 than half its bulk lay on the inner side of the superficial 

 musculature, the action of these muscles would tend to force it 

 into a deeper position, where, relieved from the pressure of the 

 shell, it would stand a better chance of growing into a perfectly 

 spherical " fine pearl." 



Preparation LXIY c, the third of these pearl-bearing examples 

 from the Persian Gulf, contained two pearls, of minute size, about 

 2 mm. apart on the left side. Each was rather less than 1 mm. 

 in diameter ; one was round, the other elongated. Both lay in 

 the subepidermal parenchyma, sepai'ated from the ovary by the 

 usual muscular sheath of the visceral mass. Both had pseudo- 

 nuclei of columnar substance. That of the more elongated one 

 is shown in PI. XLI. fig. 34. It has a central cavity, with 

 irregular granular contents (gt'-), suiTounded by a number of 

 layers of nacre (nac), outside which is a complete layer of columnar 

 substance (col.) which is coated on two sides by nacre, passing 

 over at the two poles corresponding to the longest axis of the 

 pearl into further coats of columnar substance (col.'). The 

 transition from nacre to columnar substance is very well 

 seen. 



The centre of the second pearl in this example was also 

 composed of columnar substance, formed around a central gi-anular 

 mass. The granular mass measured about '02 mm. in diameter, 

 the whole centre or pseudo-nucleus "3 mm. These preparations, 

 apart from the difiiculty of obtaining material from the Persian 

 Gulf, are of interest as showing that the nuclei or pseudo-nuclei 

 of the pearls produced by M. vulgaris in these waters do not 

 differ from those of the pearls produced by the same species in 

 Oeylon. 



B. Pearls purchased in Ceylon. 



I will now proceed to a short account of the nuclei and pseudo- 

 nuclei of the twenty-one pearls purchased in Oeylon. All of 

 these were decalcified, examined entire in oil of cloves, and 

 drawn. Eighteen of them were also sectioned. (The drawings 



