THE CEYLON PEARL-OYSTER. 343 



a central cavity, and their difference from the " Kelaiirt " class of 

 peai'ls was tl'.erefore probably due to a difl'erence in their secondary 

 growth, rather than in their primary origin. One of those 

 sectioned (Pi'eparation N. IV.) had a pseudo-nucleus composed of 

 strMtiHed columnar substance, with ijiternally some nacre siu-- 

 rouiiding a small mass of brownish granules. 



It cannot, I think, he argued in comparing these pearls with 

 Ceylon pearls that they are all seed-pearls or " muscle-pearls." 

 They occurred in all the usual parts of the external body-wall and 

 inantle, and some of them had all the properties of small " fine 

 pearls." Preparation N. VI., for example, was a beautiful little 

 spherical pearl, of high quality, measuring about 2*5 mm. in 

 diameter, which I was extremely reluctant to sacrifice in the 

 interests of science, and a number of the others were solitary 

 " parenchyma-pearls " of small size. 



H. 2'it'o Pearls from Margaritifera vulgaris //oh? the Mediterranean, 

 given to me by Professor Rapltael Dubois. 



Professor Raphael Dubois most generously placed at my 

 disposal for comparison two small pearls taken from M. vnlgaris 

 from the coast of Tunis. I'liis species has firndy established 

 itself in several parts of the Mediterranean, since the opening of 

 the 8uez Canal, having no doubt come thi-ough from the Red 8ea, 

 either in the free-swinnning larval stage or as young spat attached 

 to the bottoms of vessels. I can add nothing to what Dr. Dubois 

 has already said about the structure of these pearls, (8) pp. 103- 

 105. One contained a central body, lather less than "5 mm. in 

 diameter, which on being sectioned j^roved to be composed of very 

 homogeneous granular matter surrounded on one side l)y columnar 

 substance and on the other side by "amorphous substance." The 

 other contained a small yellowish spherical body, '08 mm. in 

 diameter, which, examined in oil of cloves, showed no recognisable 

 structure. In section it appeared to consist of a very small amount 

 of granular matter, suri'ounded by what looked like stratified 

 amorphous repair-substance. Dr. Dubois's observations have 

 shown, without doubt, that the pearls produced by this species in 

 the Mediterranean (and their single occurrence, in positions away 

 from the muscle-insertions, renders it necessaiy to treat them in 

 part at least as Parenchyma-pearls and not as Muscle-pearls) have 

 not Cestodes in their centres, but have nuclei and pseudo-nuclei 

 similar to those which 1 have described above, for pearls from the 

 same species from other localities. 



I. Pearls from M. Yu\gi\Y\?, froia Nevi Caledoniq, given 

 to me by Professor Searat. 



Professor L. O. Seurat, at my request, very kindly sent me four 

 small seed-pearls from Margaritifera vtdgaris,iroin New Caledonia, 

 and also a slide, showing a larger peai-1 from the same species 



