TIIK CEYLON rRAUL-OVSTER. .'5155 



Figure 51 shows a pearl, tlie " psoudo-uucleus " of wliicli is 

 produced out in one direction as a stivind of columnar and 

 granular repair-substance extending througli the pearl. Tliis 

 columniir substance is seen to pass over later.'dly into the ordinary 

 nacre, and no doubt corresponds to an area in the pearl-sac at which 

 the normal secretion-i)rocesse8 wei-e disturbed. Tliis was one of the 

 examples in which the ren,! nucleus broke away. 



Fig. .'?() on PI. XLll., which is the centre of the pearl shown 

 in fig. 52 (PI. XLV.), enlarged, sliows interesting ti'ansitioiial 

 substance at one pole. This is further enlarged at fig. 4.'}, 1*1. 

 XLIII. The pseudo-nucleus is seen to be discontinuous with the 

 later-depositeil shell-su])stance, a condition of things which is 

 sometimes found, and which seems to suggest a pause before the 

 epithelium becomes pi'opei'ly functional. 



Plate XLV. figs. 53 & 53 a show a pearl with a spliperocrystal- 

 like pseudo-nucleus, the longest diameter of which slightly 

 exceeded 1 mm. In this case the columnar substance was very 

 minutely reticulated and fell into three distinct zones. The 

 pearl is interesting, as showing at one side a patch of columnar 

 repair-substance apparently continuous with the nacreous layers, 

 secreted over some foreign matter (granules) that had found their 

 way into the pearl-sac during the course of the pearl's growth ; 

 this columnar substance formed a small " blister" in the substance 

 of the pearl. 



Where a sand-grain is present as nucleus, it appears to be 

 followed, as a rule, by repair- substance ; but in PI. XLV. fig. 54 

 this is hai'dly discernible, except at one pole. This was a pearl 

 which was di'awn entire, and sent to be sectioned, when it was 

 found that the nucleus broke away and resisted cutting. This 

 nucleus was returned to me, and proved to be a siliceous sand - 

 grain (fig, 54 a), measui-ing about '8 mm. in diameter. It was 

 surrounded by an opaque substance, probably " amorphous repaii-- 

 substance." 



Fig. 56 (PL XLVI.) shows a sand-gi-ain which measured 

 about '35 X "25 mm. suri-ounded first by amorphous substance, 

 then by stratified columnar substance. 



Fig. 55 (PI. XLVL), taken from a pearl which I have 

 preserved entire, shows a pyriform sand-grain, '66 X '5 mm., 

 surrounded by a thin layer of columnar substance, followed by 

 nacre. 



Figs. 37-39 (PI. XLII.) are from the capsule surrounding 

 a nucleus wliich Vji-oke away and was pi-obably a sand-gi'ain. 

 Here, again, we have first the arnoi'phous substance, passing 

 over into "colunniar" substance of sphterocrystal-like form, with 

 regular alveoli, which are approximately equal in length, breadth, 

 and depth. 



Figures illustrating minor varieties of the repair-substance as 

 it occurs in the shell, in the pearl, and in the pearl pseudo-nucleus 

 might be multiplied indefinitely, but I think enough have been 

 given to illustrate my contention that these dark sphei'ical bodies, 



