THE CEYLON PEARL-OYSTER. oa) 
ceol.’’, incomplete columnar layer; nac.'’, nacreous substance of the pearl. 
Preparation XLIII B. X 75. 
Fig. 29. Margaritifera vulgaris, Persian Gulf. Portion of the repair-substance 
formed inside the shell to close a large hole made by a borer of some kind 
in the lateral region, below the umbo. am., amorphous substance ; 
y, outer surface of repair-membrane; a, x’, cracks in the outer face of the 
amorphous substance; col., columnar repair-substance; col.’, stratified 
do.; tr., ¢r.’, transitional substance (granular repair-nacre) from columnar 
repair-substance to nacre; nae., nacre. Preparation LXXVI. xX 400. 
Vig. 29a. Margaritifera vulgaris, Persian Gulf. From a section through a blister 
on the shelJ-margin, formed over a Leuwcodore tube. am., amorphous 
repair-substance; alv., the same with alveoli containing carbonate of 
lime; pr., prismatic substance. Preparation XI. > 500. 
Pratt XLI. 
Fig. 30. Margaritifera vulgaris; Dy. Kelaart’s material. Sections showing june- 
tion between two of the constituents of a “multiple pearl,’ with the 
various abnormal products which arose in association with the disturbances 
caused by the fusion of the two pearl-sacs, and the retreat of the wedge- 
shaped plug of tissue when its connection with its fellow of the opposite 
side was broken down by the absorption or degeneration of the membrane 
separating the two pearls. p., p.’, outer nacreous layers of the two pearls ; 
rep.nac., gvanular repair-nacre; col., simple columnar substance, analo- 
gous to that found im the nuclei of some pearls; am., amorphous 
substance showing rough stratifications, perhaps corresponding to pauses 
in the retreat of the wedge of tissue; ¢7., transition from amorphous 
substance to columnar substance; ¢.’, transition from amorphous sub- 
stance to granular substance; nac.’, nacre of the compound pearl embracing 
both constituent pearls. Preparation LXXI c. X 300. 
Fig. 31. Margaritifera vulgaris. Unlabelled specimen, British Museum. One end 
of the suture between the fused-pearls shown in fig. 49, Plate XLIV. 
nac., nac.’, the nacreous layers of the two pearls; col., col.’, columnar 
substance, secreted after the epithelium had, through atrophy, lost its 
power of producing nacre; ep., ep.’, the degenerated remains of the 
epithelia of the pearl-sacs; par., the remains of the intervening paren- 
chyma. Preparation LXIJI 3B. X 350. 
Fig. 32. From the middle of the same suture; in this case the outlines of the 
parenchyma-cells, par., are still visible. ep., remains of the epithelia of 
the pearl-sacs. XX 350. 
Fig. 33. Parenchyma-pearl in situ in the tissues of Margaritifera vulgaris, from 
the Persian Gulf. _ep., outer shell-secreting epithelium ; ep.’. epithelium of 
pearl-sac ; par., subepidermal parenchyma ; g/., gland-cells in same; musc., 
muscular coat ofthe visceral mass ; musc.’, musculature to wall of stomach ; 
C.T., connective-tissue of visceral mass; ov., tubules of ovary; col., columnar 
substance forming the centre of the pearl; xac., nacreous portion of the 
pearl. Preparation LXIV B. x 80. 
Fig. 34, Centre of a pearl from another example from the Persian Gulf. gr., granular 
matter; am., (2?) amorphous substance ; nac., nacreous layer, immediately 
surrounding the “ nucleus’; nae.’, outer nacre ; col.,columnar substance ; 
col.’, imperfect layer of same, passing over laterally into nacre. Preparation 
I MIVies 5O250) 
Fig. 35. The central, spherocrystal-like pseudo-nucleus of the pearl shown in figs. 
50 & 50 4 (Plate XLV.) ; from the sample of pearls purchased in Ceylon. 
grnm., granular repair-nacre ; am., amorphous substance. Preparation 
XLUI. x 400. 
Prare XLT, 
Fig. 36. The pseudo-nucleus of the pearl shown in fig. 52 (Plate XLV.); from series 
purchased in Ceylon. g7., granular substance in central cavity forming 
the true nucleus ; am., amorphous substance ; nz., pseudo-nucleus, which 
here possesses a highly alveolar structure; co/., columuar repair-substance 
passing over laterally into nae., nacre. Preparation LIJI. » 70. 
Fig. 37. Alveolar columnar repair-substance and radially reinforced nacre, from the 
pseudo-nucleus surrounding a sand-grain (or other hard body that broke 
away) in a pearl from the same series. am., amorphous substance, forming 
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