THE CEYLON PEARL-OYSTER. 333 
of those not figured here are retained with the slides for 
reference.) 
(a) One (Preparation XLV) had no obvious nucleus or pseudo- 
nucleus. 
(>) One (Preparation XLITT) had a small spherocrystal-like 
centre of columnar substance, with no foreign contents 
(Pl. XLV. figs. 50 & 50a and Pl. XLI. fig. 35). 
(c) Three (Preparations XL, XLIV, & LIV) had what appeared 
to be irregular masses of amorphous shell-substance, in 
central cavities, passing over into repair-substance (PI. 
XLV. figs. 53 & 53a; Pl. XLVI. fig. 57; and Pl. XLII. 
fig. 40). 
(zd) Three (Preparations XLVITI, LITT, & LIV c) had central 
cavities containing more or less granular matter, the 
character of which could not be determined, but which 
suggested dead organic particles (Pl. XLV. fig. 52 and 
Pl. XLII. fig. 36). This was surrounded by repair- 
substance of columnar structure. 
(e) One (Preparation LIV 5) had in its central cavity granular 
matter in which diatoms, fragments of sponge-spicules, 
(?) minute sand-particles, and vegetable débris were present. 
These were surrounded by columnar repair-substance 
(Pl. XLITI. fig. 44). 
(f) One (Preparation LIV) had, in the otherwise indis- 
tinguishable granular contents of the central cavity, a 
fragment of a Radiolarian shell (PI. X LITT. fig. 45). 
(7) Four had undoubted sand-grains, forming the nuclei around 
which the pearl was laid down (Preparations LIT, 
LIV a, LIVu, & LIV1). The largest diameters of 
the sand-grains in these four cases measured, respectively, 
‘Sy nim., “oo x<- lomm:, “Gmm., and “3 mm. CE ee 
figs. 54 & 54a; Pl. XLVI. figs. 55 & 56). 
(x) One (Preparation LIV x) had a large spherocrystal-like 
pseudo-nucleus of repair-substance, intergrading with 
nacre, and a central cavity which had been partly 
obliterated in cutting the sections, but apparently con- 
tained several small quartz-fragments. 
(2) Six pearls (Preparations XLII, LI, LIVs, LIVp, 
LIVe, & LIV Fr) had, in their centres, bodies which 
were so hard that they broke away in sectioning, and were 
unfortunately not returned to me with the sections. The 
probable diameters of these bodies in the first five pearls 
were respectively -45mm., *2mm., ‘1 mm., -25mm., and 
“6mm. Preparation LIV Fr had a pseudo-nucleus of 
amorphous substance so dense that it broke away. In the 
eases of XLIT, LIV, and LIV a, I feel pretty sure 
that the nuclei here too were grains of sand, the others 
may have had either sand-grains or abnormally bard 
amorphous substance in their centres (Pl. XLV. fig. 51 ; 
Pl. XLII. figs. 37-39). 
[75] 
