THE CEYLON PEARL-OYSTER. BIL 
central cavity, secondary cavities in its substance, in which 
organic particles are lodged (fig. 20). 
The variations of coarsely alveolar structure which amorphous 
substance shows (e.g. Pl. XL. fig. 29 a@ and Pl. XLII. figs. 40 & 41) 
recall those structures which Biitschli (6, Taf. iii. figg. 20-33) 
describes in the spherocrystals of (?) Trydimite formed when the 
siliceous concretionary substance of the Bamboo (known as Tabaxir 
or Tabasheer) is heated ; this structure is probably in great measure 
the expression of the physical conditions (surface tension, etc.) 
which prevail when two substances in solution or in a colloidal 
state separate from one another to form a spherocrystalline 
mass. 
Pl. XLII. figs. 37 & 39 are of interest as showing another 
variation of the nacre, in the direction of columnar substance. 
In this variety of nacre, the conchyolin-layers are connected 
by a number of thickened junctions, which tend to occur 
in groups and which are arranged in radial rows. In surface 
view these junctions appear as groups of dark spots on the 
conchyolin-layers ; in radial section they are as shown in fig. 37, 
and can also be seen in Pl. XX XVI. fig. 13. These junctions 
seem to be thickenings of the walls which normally connect 
the several conchyolin-layers of the nacre to one another; they 
may, in fact, be regarded as local exaggerations of the condition 
described as “ granular repair-nacre.” 
It is interesting to note the peculiar manner in which these 
repair- _substances occur in Japanese “Culture Pearls.” ‘This 
name was given by the late Professor Mitsukuri (27 ¢, pp. 283-4, 
pl. xi. fig. 1) to pearl-like bodies—‘ blisters,” as they would be 
called on the Australian fisheries—which are artificially produced 
in the Japanese Pearl-Oyster, Margaritifera martensii * Dunker. 
The production of these “‘ Culture Pearls” is an extensive 
industry supporting about 100 persons, and is carried on by 
Mr. Mikimoto on leased areas of sea-bottom in the Bay of Agu, 
Shima Province, on lines originally suggested by Prof. Mitsukuri 
in 1890. It has been going as a commercial success since 1898, 
when the first crop of ‘ Culture Pearls” was marketed. In 1905 
the number of oysters operated on per year was from 250,000 to 
300,000. 
The process, which is protected by patents, is analogous to that 
adopted by the Chinese in the production of “ Buddha Pearls” 
in the fresh-water mussel, Dipsas plicatus, and to the method 
discovered by Linnzeus in the 18th century (see Herdman, 16 a), 
and consists in the introduction between the shell and the mantle 7 
of a bead of nacre, which in due course (the time allowed in 
Japan is four years) becomes thickly coated over with nacre, 
* This molluse is regarded by some naturalists as a local race of M, vulgaris, to 
which it is undoubtedly very closely related. Whether it be called WM. martensii or 
M. vulgaris var. martensii is largely a matter of individual taste. 
+ This is apparently done vid the edge of the shell and not by drilling as in the 
Linnzeus process. 
[59j 
