THE CEVLON PEARL-OYSTER. ?>')~J 



roL", incninplete columiiav 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 tlie lateral region, below the umbo. am., amorphous substance ; 

 .V, outer surface of repair-membrane ; x, x', cracks in the outer face of the 

 :imori)hous sul)stancu; col., columnar repair-substance; col.', stratified 

 do. ; tr., tr.' , transitional substance (granular repair-nacre) from columnar 

 repair-substance to nacre ; nac, nacre. Preparation LXX VI. X 400. 



Fig. 29 (T. liargaritifera vulgaris, Persian (Julf. From a section through a blister 

 oil the shell-margin, formed over a Leucodore tube, am., amorphous 

 repair-substance; ali\, the same with alveoli containing carbonate of 

 lime; /(>•., })rismati(' substance. Preparation XI. X .500. 



Plate XLI. 



Fig. 30. Margaritifera vulgaris; Dr. Kelaart's material. Sections showing junc- 

 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., granular repair-nacre; col., simide columnar substance, analo- 

 gous to that found in the nuclei of some pearls ; aw., amorphous 

 substance showing rough stratifications, perhaps corresponding to pauses 

 in the retreat of the wedge of tis.sue; tr., transition from amori)hons 

 substance to columnar substance; tr.', transition from amorphous sul)- 

 stance to granular substance ; nac.', nacre of the compound pearl embracing 

 both constituent pearls. Preparation LXXI c. X 300. 



Fig. 31. Ilargaritifera 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 LXIII b. X 350. 



Fig. 32. From tlie middle of the same suture ; in this case the outlines of the 

 ])arencbyma-cells, par., are still visible, ep., remains of the epithelia of 

 the pearl-sacs. X 350. 



Fig. 33. Parenchyma-pearl ?■» S(7?(, in the tissues of Margaritifera vulgaris, from 

 the Persian Gulf, ep., outer shell-secreting epithelium ; ep.', epithelium of 

 l)earl-sac ; jyar., subepidermal parenchyma ; _g'^, gland-cells in same ; mnsc, 

 muscular coat of the visceral mass ; »«h.9c.', musculature to wall of stomach ; 

 r.T"., connective-tissue of visceral mass; o?)., tubules of ovary; co?., columnar 

 substance forming the centre of the pearl ; nac, nacreous portion of the 

 I)earl. Preparation LXIV B. X 80. 



Fig. 34. Centre ofa pearl from another example from the Persian Gulf, gr., granular 

 matter; am., (?) amorphous substance; nac, nacreous layer, immediately 

 surrounding the " nucleus " ; nac.', outer nacre ; col., columnar substance ; 

 col.', imperfect layer of same, passing over laterally into nacre. Preparation 

 LXIV c. X 250. 



Fig. 35. The central, spha-rocrystal-like pseudo-nucleus of the pearl shown in figs. 

 50 & 50 ,\ (Plate XLV.) ; from tlio sample of pearls purchased in Ceylon. 

 (/r.ii., granular repair-nacre ; am., amorphous substance. Preparation 

 XLIII. X 100. 



Plate XLI I. 



Fig. 30. The pseudo-nucleus of the pearl shown in fig. 52 (Plate XLV.) ; from series 

 |)urchased in Ceylon, gr., granular substance in central cavity forming 

 the true nucleus ; am., amorphous substance ; nu., pseudo-nucleus, which 

 here possesses a highly alveolar structure ; col., columnar repair-substance 

 passing over laterally' into nac, nacre. Preparation LIII. X 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 

 awav) in a pearl from the same series, am., amorphous substance, forming 



23* 



