oon 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 (Pl. XLI. fig. 33) the pearl is seen 
to le in the subepidermal parenchyma (par. ), projecting a littie 
through the muscular coat (msc.) into the visceral connective- 
tissue “(c .t.), 12 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 the 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 
spheri ical ‘‘ fine pearl.” 
Preparation LXIV c, the third of these pearl-bearing examples 
from the Persian Gulf, contained two pearls, of minute size, about 
2mm. 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, separated 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 Pl. XLI. fig. 34. It has a central cavity, with 
irregular granular contents (gr.), surrounded by a number of 
layers of nacre (2ac.), 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 granular 
mass. ‘The granular mass measured about ‘02 mm. in diameter, 
the whole centre or pseudo-nucleus °3 mm. These preparations, 
apart from the difficulty 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 
Ceylon. 
B. Pearls purchased in Ceylon. 
T will now proceed to a short account of the nuclei and pseudo- 
nuclei of the twenty-one pearls purchased in Ceylon. All of 
these were decalcified, examined entire in oil of cloves, and 
drawn. Eighteen of them were also sectioned. (The drawings 
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