THE CEYLON PEARL-OYSTER. 357 
showed that here again the real nucleus was a cavity containing strands 
or sheets of conchyolin-like substance and a few granular bodies, perhaps 
of cellular origin (Plate XXXVIIL. fig. 18); while the dark appearance 
of the central mass was due to the interpolation between the proper 
poe layers ofan abnormal patholegical product. Preparation LX XI s. 
X 27. 
Fig. 49. A double pearl from one of the unlabelled specimens in the British Museum; 
decalcified, cleared, and examined entire. The nucleus of the left-hand 
constituent is figured on Pl. XL. fig. 28, the characters of the substance 
at the suture between the two pearls at figs. 31 & 32 on Plate XLI. In 
the pseudo-nuclei of these pearls the columnar substance is stratified. 
Preparation LXIII Bp. X 27. 
PLATE XLY. 
Figs, 50, 50 a. The central portion of a white porcellanous spherical pearl, from the 
sample of pearls purchased for me in Ceylon by the Ceylon Company of 
Pearl Fishers, Ltd. Fig. 50, decalcified and examined whole in oil of 
cloves. Here the nucleus, when examined whole, might well be mistaken 
for a small Trematode. Fig. 50 a. Section through the centre of the same 
pearl. The pseudo-nucleus is seen to consist of an irregular nacreous body, 
shown in fig. 35 (Plate XLI.) to be granular repair-nacre, surrounding a 
minute spherocrystal-like mass; about 0°08 mm. in diameter. Pro- 
paration XLII. x 27. 
Fig. 51. Another pearl from the same collection. An oval pearl, of fine quality, 
35 mm. X 3mm. in diameter. This pearl shows a tract of stratified 
columnar and granular repair-substance, extending outwards from the 
pseudo-nucleus and passing over laterally inte the nacre, Preparation LI. 
x 20. 
Fig. 52. Another pseudo-nucleus, from a pearl in the same collection. This was a 
small spherical pearl of fine quality, about 2 mm. in diameter. The 
columnar substance here, ced., is alveolar in structure, and surrounds a 
central cavity containing afew granules. Fora section of the centre of this 
pearl, see fig. 36 (Pl. XLII.) Preparation LIT. X 27. 
Figs. 53, 53a. Centre of another pearl from the same series. The pearl was oval, 
about 3 mm. in diameter, with a faint zonar constriction and a rather 
coppery tint. Examined entire (fig. 50) it shows a large pseudo-nucleus, 
over a millimetre in diameter, which falls into three layers. It also shows 
a blemish in the nacre, coated over with repair-substance. Fig. 53 @ 
shows the same in section, The columnar repair-substance is finely 
reticulated or alveolar. The blemish is caused by a few granules, which 
have found their way into the pearl-sac and have been covered over with 
columnar repair-substance, which passes over laterally into ordinary nacre, 
Preparation LIV. X 27. 
Figs. 54,54 a. Fig. 54. Central portion of another pearl, which measured about 
3mm. X 2°75 mm. A pearl of fine colour, but with slightly irregular 
surface. The nucleus of this pearl is a sand-grain, enclosed in an opaque 
yellowish coat, probably consisting of repair-substance, At one pole is 
seen a process of repair-nacre, but, except for this, no columnar substance 
appears to surround the grain. Vig. 54a. The sand-grain, dissected out 
from the above preparation. Preparation LIT. ™X 27. 
PratE XLVI. 
Fig. 55. Fine spherical pearl, from the same series, about 2 mm. in diameter. 
Nucleus a grain of sand surrounded by a thin layer of columnar substance, 
thickened at one pole. Preparation LIV mw. xX 27. 
Fig. 56, Another pearl from the same series, a small spherical pearl about 2 mm. in 
diameter. ‘The nucleus is a grain of sand, forming the centre of a typical 
pseudo-nucleus of columnar substance. Preparation LIV a. X 27. 
Fig. 57. A brown pearl, spberical, 3 mm. in diameter, formed of the prismatic 
substance. From thesame collection. xw., pseudo-nucleus; co/., columnar 
substance ; am., amorphous substance; co/.’, fine columnar-prismatic sub- 
stance ; pr., ordinary prismatic substance ; 4/., blister formed over intrusive 
foreign matter. For the several substances of this pearl, more highly 
magnified, see Plate XLII. figs. 40-42. DPreparation Xl. X 27. 
Ss. 
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