THE CEYLON PEARL-OYSTER. 319 
particular sections that I examined, there was a marked absence 
even of the repair-substances. But in the zone immediately 
around the point of contact between nucleus and shell, where, 
when the nucleus was introduced, the epithelium of the mantle 
was presumably unable to fit closely against the surfaces, it is 
otherwise. Here, on examining the whole “ Pearl” as a trans- 
parent object after decalcification, an opaque ring or zone was 
distinctly visible. This was due to the presence of granular 
matter, perhaps derived from the exterior, perhaps from the 
tissues of the animal (text-figs. 39 & 40 B, gr.), and to very 
irregular columnar and amorphous repair-substance (col., col.’). 
his columnar substance is shown in greater detail in text-fig. 40, 
A & B, corresponding respectively to col. and col.’ in text-fig. 39. 
In text-fig. 40, A, in the niche between the nucleus and the shell, 
where the mantle-epithelium could not reach, we see the product 
of its secretion consolidated away from the influence of the 
epithelium. Here the columns, instead of forming the character- 
istic palisade-lhke structure, with their long axes perpendicular 
to the secreting surface, are arranged in groups suggesting 
incomplete spheerocrystals. 
The curious fan-like arrangement which the columns take on in 
text-fig. 40, B, suggests that the repair-substance arose through an 
extravasation of the shell-forming fluids at the point a, the layer 
nac.' representing the first normal nacre, secreted by the mantle 
when it occupied that position, the irregular columnar and 
amorphous substance being due to the consolidation of the 
secretion which filled the space, triangular in section, which lay 
between the nucleus (nw.), the shell (nac.), and the mantle; the 
position occupied by the last named being represented by the layer 
of nacre marked nac’. 
(13) Varrerres or Ceyton Prarts. 
Pending a classification based on the nature of the causes 
which give rise to the formation of the pearl-sac, I propose, 
following Herdman, to separate the pearls which I have examined 
in or from the Ceylon Pearl-Oyster into two main groups, 
accordingly as they typically occur clustered in the neighbourhoods 

really satisfactory proof has ever been given that free spherical “pearls” can be 
produced in this way, though Prof. Mitsukuri (/.c.) says that there are some hopes 
that this will be done. There is no theoretical reason why a modification of the 
Japanese or Linnean operation should not be devised which would achieve this end— 
indeed, there is some reason to think that Linneus actually did produce some round 
“pearls” and not only “blisters.” But such bodies, if produced, would not be 
“pearls” in the strict biological sense, though it is quite likely that they would be 
marketed as such in quantities before the difference was detected. 
Since writing the above, I have been informed by Mr. 'Toyozo Kobayashi, Professor 
at the Tokyo Higher Technological College, who is associated with Mr. Mikimoto 
in his enterprise, that perfectly free “ pearls” have been produced by these methods 
within the last two years, but so far only exceptionally, and on a scale so small as 
not to be applicable commercially. 
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