356 DR. H. LYSTER JAMESON ON 
the innermost layer of the columnar pseudo-nucleus, col. ; nac., nacre 
nac.’, radially marked, catenuiated variety of nacre, characterised by 
radial rows of junctions which occur in small groups between conchyolin- 
layers (june.); nac.’’, the normal nacre, passing over into this specialised 
variety of nacre. Preparation LIV @. X 300. 
Fig. 38. Tangential section through the alveolar-columnar substance shown at 
col, in tig. 37. XX 300. 
Fig. 39. Tangential section through the radially catenulated repair-nacre, shown at 
nae.’ in fig, 87. june., the groups of junctions in radial rows, seen in 
surface view. The section is near the inner surface of this layer. X 300. 
Fig. 40. Centre of the imperfcetly decalcified brown pearl, shown in Pl. XLVI., 
fig. 57. nu., nucleus with rhombohedra of calcite ; am.’, lining of 
amorphous substance; col., columnar layer; col.tr., transition-layer from 
alveolar-columnar substance to amorphous substance; am., amorphous 
substance, with scattered alveoli, containing calcium carbonate. Pre- 
paration XL. X 280. 
Fig. 41. Part of the same pearl, external to that shown on fig. 40, showing the 
transition from amorphous substance, am., with scattered alveoli, through 
an intermediate substance, ¢7., to needle-like prismatic substance, col. 
xX 250. 
Fig. 42. Transition from the needle-like prismatic substance, col., shown in fig. 41, 
to the ordinary prismatic shell-substance, p., similar to that of the shell. 
al., minute alveoli in the thickenings of the walls of the prisms, similar 
to those observed by Rémer (82). X 2650. 
i Pruate XLITI. 
Fig. 43. A portion of the repair-substance in the body of a pearl, shown at col. 
in fig. 386, showing transitions from amorphous substance to nacre. 
nu., outer part of the pseudo-nucleus; am., amorphous substance, with 
alveoli, which passes over into finely columnar substance, co/. This 
in turn goes over through granular repair-nacre, g7., into normal nacre, 
nac.’, and is followed by layers of normal nacre (nac.) externally. Pre- 
paration LIT. x 400. 
Vig. 44. Portion of the contents of the central cavity of one of the pearls purchased 
in Ceylon; showing also a portion of the columnar substance which 
surrounded the centre. The contents drawn are selected from a number 
of the sections in the series cut from this specimen. ae., nacreous 
substance of the pearl; col., columnar repair-substance surrounding the 
nucleus; am.,am.’, anorphous substance; dia., diatoms; spic., fragments 
of sponge-spicules ; veg., vegetable débris. Preparation LIV 3. XX 500. 
Fig. 45. Fragment of a Radiolarian shell, from the centre of another of the same lot 
of pearls. Preparation LIV 5. X 600. 
PiatEe XLIV. 
Figs. 46, 46 a. Pearl from a cluster of pearls in one of Dr. Kelaart’s specimens. 
Decalcified and examined, 46, entire in oil of cloves, 46a, in section. The 
diameter of the pearl was just 2 mm., that of the central denser part was 
13mm. There is a simple central cavity. Preparation XVI. XX 27. 
Figs. 47, 47 a. Another pearl from Dr. Kelaart’s material, decalcified and examined, 
47, entire, and, 47 @, in section. The diameter of the pearl was 2 mm. ; that 
of the dark, opaque, yellowish centre rather over 1 mm. Examined entire 
the nucleus appears amorphous, and might well be mistaken for the dead 
remains of a parasite; but this peculiarity was found, on sections being 
made, to be due to a break in the continuity of the nacreous layers 
and the interpolation of a dark layer, composed of irregularly calcified 
conchyolin, and granules which are probably of extraneous origin. ‘There 
is a small central cavity, as in the rest of Dr. Kelaart’s pearls, with a plug 
of conchyolin-like substance at one side. g7., granular dead matter; col., 
columnar substance; 2, nacre. Preparation XV. X 27. 
Fig. 48. A “double” pearl from Dr. Kelaart’s material, decalcified, cleared, and 
examined entire. Sections through this pearl are shown on Plates 
XXXVII. & XXXVIII. figs. 16-18. The pearl was 2°25 nm. in diameter. 
The pseudo-nucleus was a dark opaque body, about 0° mm. in diameter, 
similar to that shown in fig. 47, and might easily be taken, on examination 
of the entire pearl, for the shrivelled remains of a dead parasite. Sections 
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