314 DR. H. LYSTER JAMESON ON 
and formed coarsely stratified amorphous substance (am.), broken 
by cleft-like cavities. Later on, when the retreat of the plug 
of tissue was less rapid, this amorphous substance passed over 
into columnar substance (é.) and granular repair-nacre (¢r.'), and 
finally gave place to the nacre (nac.’) of the common investment 
of the compound pearl. 
The columnar repair-substance varies enormously, and passes 
over imperceptibly into “amorphous substance” or lime-free 
conchyolin, granular repair-nacre, ordinary nacre, and the 
prismatic substance of the shell. For example, the repair- 
membrane, a part of which is shown in Pl. XL. fig. 29, showed 
an immense number of variations from place to place. In some 
parts a second layer of amorphous substance was interpolated 
between the columnar layers; in others the columnar substance 
passed over into a coarsely alveolar substance with irregular 
cavities, some of which penetrated into the amorphous substance. 
In yet other spots the amorphous substance passed over through 
granular repair-substance into nacre. 
Columnar substance is frequently stratified, consisting of a 
number of consecutive layers. This is seen at col.’ in the repair- 
membrane figured at fig. 29. It is also shown in the pseudo- 
nucleus of the pearl shown on Pl. XL. fig. 28 and Pl. XLIV. 
fig. 49, and in the pearls from the Persian Gulf in Pl. XLI. 
figs. 33 & 34, In the former of these last-named instances it 
occurs immediately around the central cavity, in the latter case 
interstratified and intergrading with the nacre. 
Im Pl. XOLIID. fig, 43 *(col.) it is seen passing over on the one 
hand into granular repair-nacre, on the other into amorphous 
repair-substance. ‘The same stratified columnar substance is well 
shown in Pl. XLV. fig. 51, where it forms a curious flaw running 
through the substance of a pearl. 
Apart from this direct stratification, the columnar repair- 
substance may have an internal alveolar structure such as is 
shown in Pl, XLII. figs. 36, 37, & 38. Figs. 40-42 on the same 
Plate, taken from the pearl shown in Pl. XLVI. fig. 57 (a brown 
pearl composed of prismatic shell-substance), show the transition 
from amorphous repair-substance to columnar repair-substance 
(figs. 41, 42, col.), and from the latter to the prismatic layer of 
the shell (fig. 42, pr.). 
The third variety of repair-substance I call amorphous repair- 
substance. In its typical form this substance is seen at am. in 
Pl. XL. fig. 29, where it is obviously the result of the first effort 
of the mollusc to close the injury to the shell, and in Pl. XLI. 
fig. 30, where it is the product of a fully functional epithelium, 
retreating rapidly and leaving its secretion in its wake. It shows 
little or no structure under ordinary magnifications, but is usually 
faintly stratified. Jt may contain cavities, arranged in rows 
parallel to the secreting-surface, and with at times also a radial 
arrangement. ‘These cavities typically contain carbonate of lime. 
Pl. XL. fig. 29 @ (Margaritifera vulgaris, Lingah Shell, Persian 
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