9i; 



SEALE. 



and that of the (Jeylon mother-of -pearl, as given by Herdman and 

 Hornell ^° is — 



Calcium carlioiiiite Ss.79 



Calcium sulphate 4.93 



( )rganic matter 2.32 



Water 2.28 



Loss (no magnesium, no pliospliates, faint trace 



of iron) 1.68 



It is well kiioMii that the organic basis of the shell, eonchiolin, is a 

 eutieular product e.xcrcted by the 'underlying epideiinis of the mantle. 



Pas.sing without comment the many fanciful theories regarding the 

 formation of pearls which have been held from historic times up to a 

 comparatively lecent date, we will consider only sucli facts as have been 

 revealed by modern scientific investigation. 



I have in my work dissected a large number of pearls from our large 

 gold lip pearl oyster (i)/. maxima Jamson). Of this number, forty were 

 prepared as "hard sections/' each side being ground down so that a 

 small transparent section through the center of the nucleus was obtained 

 for mieioscopic examination. (See Plate \, figs. 1 to 3.) Ten were 

 prepared as microtninic sections, and the remainder, and by far the 

 greatest number, were dissnlved in acids of various kinds and dissected. 



'Vhi' results show that tlie round orient 

 Philippine pearl may have various ob- 

 jects in the center forming the so-called 

 nuclei, which, tecanse of stimulation or 

 irritation, have become incased in nacre, 

 thus forming jx-avls. Fully "lO per cent 

 of the pearls examined contained larval 

 cestoiles, two only contained sand, one 

 a liit of seaweed, one a spicule of calca- 

 reous sponge, two, forms which with but 

 little doubt were larval Disiomids. One 

 rather interesting form (^ee lig. 'i) ob- 

 tained from a perfectly round pearl ap- 

 jX'iirs Neiy closely to le^emljle the free- 

 swimming lar\al eeslodes secured by Mr. 

 Hornell in Ceylon, ^^ and is doubtless a 

 related form. Se^eral pearls contained 

 material that had become calcified and could not be identified with any 

 degi-ee of certainty. Three had what I believe to be the ova of the small 



"Report of the government of Cijloii on the pearl fisheries of the Gulf of 

 Manaar. Roy. Soc. London (1906), Part V, 6. 



"Hornell & Sliiplc}'. Reports on Parasites of the Pearl (Jvster. Rep. Cciilon 

 I'corl Fishery (1003-1906), Part 11, 77; Part III, 49; Part v! 43. 



Fig. 2.- 



-Cestode from center of a Phil- 

 ippine pearl. 



