96 



SEALE. 



and that of 

 Hornell " is- 



tlie Ceylon mother-of-pearl, as given by Herdman and 



Calcium carbonate 

 Calcium sulphate 

 Organic matter 

 Water 



Loss (no magnesium, 

 of iron) 



no phosphates, faint trace 



88.79 

 4.93 

 2.32 



2.28 



1.68 



couchiolin. 



It is well known that the organic basis of the shell, 

 cnticular product excreted by the underlying epidermis of the mantle. 



Passing without comment the many fanciful theories regarding the 

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

 comparatively recent date^ we will consider only such 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 (M. maxima J a,T[i&on) . 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 microscopic examination. (See Plate Y. figs. 1 to 3.) Ten were 

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

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



The results show that the round orient 

 Philippine pearl may have various ob- 

 jects in the center forming the so-called 

 nuclei, which, liecause of stimulation or 

 irritation, have become incased in nacre, 

 thus forming pearls. Fully 50 per cent 

 of the pearls examined contained larval 

 cestodes, two only contained sand, one 

 a bit of seaweed, one a spicule of calca- 

 reous sponge, two, forms which with but 

 little doubt were larval Distomids. One 

 rather interesting form (see fig. 2) ob- 

 tained from a perfectly round pearl ap- 

 pears very closely to resenible the free- 

 swimming larval cestodes secured by Mr. 

 Hornell in Ceylon,^^ and is doubtless a 

 related form. Several pearls contained 

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

 degree of certainty. Three had what I believe to be the ova of the small 



'" Report of the government of Ceylon on the pearl fisheries of the Gulf of 

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



^ Hotnell & Shipley. Reports on Parasites of the Pearl Oyster. Rep. Ceylon 

 Pearl Fishery (1903-1906), Part II, 77; Part III, 49; Part V, 43. 



-Cestode from center i 

 ippine pearl. 



