314 DR. H. LYSTER JAMESON ON 



and formed coarsely stratified amoi'phous 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 {ti\) and granular repair-nacre (tr.' ), and 

 finally gave place to the nacre {nac.') of the common investment 

 of the compound pearl. 



The coUimnar 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 PI. 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 amorphoiis 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 PI. XL. fig. 28 and PI. XLIV. 

 fig. 49, and in the pearls from the Persian Gulf in PI. 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. 



In PI. XLIII. fig. 43 [col.) it is seen passing over on the one 

 hand into granular repair-nacre, on the other into amoi^phous 

 repair-substance. The same stratified columnar substance is well 

 shown in PI. 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 PI. XLII. figs. 36, 37, & 38. Figs. 40-42 on the same 

 Plate, taken from the pearl shown in PI. XLYI. 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 ain. in 

 PI. XL. fig. 29, where it is obviously the result of the first efibrt 

 of the mollusc to close the injury to the shell, and in PI. 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. It 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. 

 PI. XL. fig. 29 a (Margarififera vulgaris, Lingah Shell, Persian 



