612 Dr. G. Harley. The Structural Arrangement of the 



" The Structural Arrangement of the Mineral Matters in 

 Sedimentary and Crystalline Pearls." By GEORGE HARLEY, 

 M.D., F.R.S*. Received March 6, Read March 28, 1889. 



(Abstract.) 



The author began by giving a sketch of what has hitherto been 

 written on pearl structure, and pointed out that since Rondelet* 

 threw out the idea that pearls are merely diseased concretions 

 occurring in the Mollusca in the same way as other morbid calculi 

 occur in the Mammalia, and R^aumurf said they are misplaced 

 pieces of organised shell, in the same way as loose cartilages in human 

 joints are misplaced portions of the cartilaginous structures sur- 

 rounding them, the opinions of all subsequent writers have but 

 oscillated between these two antagonistic theories. The two chief 

 exponents of pearl structure in modern times Meckel in 1856,^ and 

 M6bius in 1858 have ranged themselves on opposite sides ; the 

 former advocating the views of Rondelet, the latter espousing those of 

 his opponent Reaumur; while Bronn,|| a still more recent writer, has 

 evidently a difficulty in deciding which of the theories is the correct 

 one. For, while the whole tenour of his remarks leads one to believe 

 that he favours the shell-formation theory of Reaumur, he speaks of 

 pearls as being lime concretions (Kalk-Konkretionen) , and pearl-like 

 calculi (Perlen-artige Konkrementen) , which he would be unlikely to 

 do were he firmly convinced in the validity of Reaumur's theory. 



It is thus seen that it is still an unsettled question whether pearls 

 belong to the animal or the mineral kingdom. And no one who has 

 worked at the subject, and knows its intricacy, can be the least 

 surprised at our very best authorities being still unable to decide as 

 to which of the two antagonistic theories is the best. For, while 

 there are undoubtedly many potent data in favour of each view, 

 there are, at the same time, not a few grave objections in the way of 

 a ready acceptance of either, as the following facts prove : 



1. As was demonstrated by the exhibition of specimens, many 

 pearls (off-coloured ones) of the sedimentary variety so closely 

 resemble the carbonate of lime calculi met with in the Mammalia, and 

 the carbonate of lime pisolite concretions from the mineral waters of 

 Carlsbad, as to be absolutely undistinguishable from them, either by 

 the naked eye or with the aid of a microscope. 



* ' Univers. Aquatil. Hist.,' 1554. 



f Mem. de 1'Acad. d. Sci.,' 1717. 



J ' Mikrogeologie : Ueber die Concrementen im thierischen Organismus,' Berlin, 

 1856. 



' Die Echten Perlen : ein Beitrag zur Luxus, Handels- und Naturgeschichte 

 derselben,' Hamburg, 1858. 



|| ' Weichthiere,' Leipzig, 1862, " Perlen-Bildung," p. 423. 



