312 DR. H. LYSTER JAMESON ON 



of being coated over with nacre. The same substance is well 

 shown in PI. XLI. fig. 35 and PI. XLIII. fig. 43 {gr.). In the 

 last-named case it 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 sub,stance 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 rods 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 calcium cai-bonate is removed by acids, and a section is 

 cut at right angles to the surface, presents a palisade-like apj)ear- 

 ance, due to the septa of conchyolin between the calcareous rods 

 (PI. XL. fig. 29; PI. 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 PI. XL. fig. 29 it is seen in the repair-membrane 

 formed over an injury caused to the shell by a boring parasite. 

 In PI. 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 shown in PI. XLIV. 

 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 sej^arated the two pearls. 



* While these substances are perhaps not strictly separable respectively on 

 chemical and phj^sioloo-ical grounds, I think it is well on uioi-phological and patho* 

 logical grounds to emphasize the distinction. 



