THE CEYLON PEARL-OYSTEU. 357 



showed that liinr njiiiiu tlie real nucleus was a cavity coutaiuiiif;- slrauds 

 or sheets ot coiichyoliii-like substance and a few jrramilar bodies, iierlians 

 of celluhu- onf,'iu (Fhite XXXVIII. tig. 18) ; while the dark ap))earance 

 of the central mass was due to the interpolation between the proper 

 naoreous layers of an abnormal pathological product. Preiiaration LXX I j 

 X 27. 

 Fig. 49. A double pearl fromoneof the unlabelled specimens in the British Museum; 

 decalcified, cleared, and examined entire. The nucleus of the left-hand' 

 constituent is tifiured on PI. XL. fig. 28, the characters of the substance 

 at the suture between the two pearls at figs. 31 & 32 on l^late XLI. In 

 the pseudo-nuclei of these pearls the columnar sulistance is stratified 

 Preparation LXIII b. X 27. 



Plate XLV. 



Figs. ;')(», 50 a. The central portion of a white porcellanous spherical pearl, from the 

 sample of pearls i)urchased 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 Ti ematode. 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 XLL) to be granular repair-nacre, surrounding a 

 minute spha;rocrystal-like mass; about 0-08 mm. in diameter. Pre- 

 paration XLI 1 1. X 27. 

 Fig. 51. Another pearl from the same collection. An oval pearl, of fine quality, 

 3-5 mm. X 3 mm. in diameter. This pearl shews a tract of stratified 

 columnar and granular repair-substance, extending outwards from the 

 ))seudo-nucleus and passing over laterally into the nacre. Preparation LL 

 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, col., is alveolar in structure, and surrounds a 

 central cavity containing a few granules. For a section of the centre of this 

 pearl, see fig. 36 (PI. XLH.) Preparation Llll. X 27. 

 Figs. 53, 53 a. Centre of another pearl from the same series. The pearl was o\al, 

 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 rnillimetre in diameter, which falls into three layers. It also shows 

 a blemish in the nacre, coated over with repair-sulistance. Fig. 53 a 

 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 pas.ses over laterally into ordinary nacre 

 Preparation LIV. X 27. 

 Figs. 54, 54 a. Fig. 54. Central portion of another pearl, which measured about 

 3 mm. X 275 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. Fig. 54a. The sand-grain, dissected out 

 Irom the above preparation. Preparation LI I. X 27. 



Plate XLVl. 



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 u. X 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 

 jiseudo-nucleus of columnar substance. Preparation LIV a. X 27. 



F^ig, 57. A brown pearl, spherical, 3 mm. in diameter, formed of the prismatic 

 substance. From the same collection, hm., pseudo-nucleus; co/., columnar 

 substance ; «>«., amorphous substance; col.', fine columnar-prismatic sub- 

 stance ; pr., ordinary prismatic substance ; hi., blister formed over intrusive 

 foreign matter. F'or the sexeral substances of this pearl, more highly 

 magnified, see Plate XLII. figs. 40-42. Preparation XL. X 27. 



