ty 
— 
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DR. H. LYSTER JAMESON ON 
of being coated over with nacre. The same substance is well 
shown in Pl. XLI. fig. 35 and Pl. XLITI. fig. 43 (gr.). In the 
last-named case if is seen to pass over on the one hand into 
nacre, on the other into columnar and amorphous repair- 
substances. 
The next form of repair-substance is much more variable, 
and occurs in several distinct, though intergrading forms. I 
propose to call this “columnar repair-substance,” in view of the 
calcium carbonate being crystallised in columns. 
Columnar substance resembles, more or less, the prismatic 
layer of the shell—indeed, it is probable that Rubbel (33, p. 171) 
had. a substance analogous to this columnar substance before 
him when he stated that the outer epithelium of the mantle 
of Margaritana is capable, in repairing the shell, of producing 
the prismatic substance which is normally only the product of 
the mantle-margin. (In the same way, he treats as ‘“ peri- 
ostracum” the non-calcified material secreted under similar 
conditions, which I describe below as ‘amorphous repair- 
substance ”’.) * 
In its simplest form columnar repair-substance consists of 
parallel needle-like reds of carbonate of lime (which Steinmann 
(43), speaking of Harting’s bodies, has aptly called “ fibro- 
crystalline ”) deposited in an organic conchyolin-matrix, which, 
when the caleium carbonate is removed by acids, and a section is 
cut at right angles to the surface, presents a palisade-like appear- 
ance, due to the septa of conchyolin between the calcareous rods 
(Pl. XL. fig. 29; Pl. XLI. fig. 30, col.). In horizontal section 
this conchyolin has a honeycomb-like structure. 
All kinds of variations occur in the coarseness or fineness 
of the calcareous elements and the organic framework. 
This substance is frequently formed on the surface of the 
shell or of a pearl when disturbances arise in the rhythm of shell- 
secretion. In Pl. XL. fig. 29 it is seen in the repair-membrane 
formed over an injury caused to the shell by a boring parasite. 
In Pl. XLI. fig. 30 it is seen (col.) in the angle between the 
surfaces of two pearls which have become secondarily attached 
together. 
Pl. XLI. fig. 31 shows the same substance developed under 
conditions similar to those existing in fig. 30. This figure is 
a drawing of a section through the suture between two pearls 
which have become secondarily fused together. The pearls 
themselves, with the intervening suture, are elton moan! 1] eXelnive 
fig. 49; the end of the suture, where the curvatures of the two 
pearls diverge, in fig. 31. In the entire object, examined in 
oil of cloves ‘(fig. 49), the suture was represented by a yellowish- 
brown line, the colour being due to the dead remains of the 
cellular membrane which originally separated the two pearls. 
* While these substances are perhaps not strictly separable respectively on 
chemical and physiological grounds, I think it is well on morphological and patho- 
logical grounds to emphasize the distinction. 
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