THE CEYLON PEARL-OYSTER. 335 
Figure 51 shows a pearl, the “ pseudo-nucleus” of which is 
produced out in one direction as a strand of columnar and 
granular repair-substance extending through the pearl. This 
columnar substance is seen to pass over laterally into the ordinary 
nacre, and no doubt corresponds to an area in the pearl-sae at which 
the normal secretion-processes were disturbed. ‘This was one of the 
examples in which the real nucleus broke away. 
Fig. 36 on Pl. XLII, which is the centre of the pearl shown 
in fig. 52 (Pl. XLY.), enlarged, shows interesting transitional 
substance at one pole. This is further enlarged at fig. 43, Pl. 
XLIII. The pseudo-nucleus is seen to be discontinuous with the 
later-deposited shell-substance, a condition of things which is 
sometimes found, and which seems to suggest a pause before the 
epithelium becomes properly functional. 
Plate XLV. figs. 53 & 53a show a pearl with a spherocrystal- 
like pseudo-nucleus, the longest diameter of which slightly 
exceeded 1mm. 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 Pl. XLV. fig. 54 
this is hardly discernible, except at one pole. This was a pearl 
which was drawn 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 bea siliceous sand- 
grain (fig. 54a), measuring about "8mm. in diameter. It was 
surrounded by an opaque substance, probably “ amorphous repair- 
substance.” 
Fig. 56 (Pl. XLVI.) shows a sand-grain which measured 
about *385 x °25 mm. surrounded first by amorphous substance, 
then by stratified columnar substance. 
Fig. 55 (Pl. XLVI.), 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 (Pl. XLII.) are from the capsule surrounding 
a nucleus which broke away and was probably a sand-grain. 
Here, again, we have first the amorphous substance, passing 
over into “columnar” substance of spherocrystal-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 spherical bodies, 
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