THE CEYLON PEARL-OYSTER. 343 
a central cavity, and their difference from the ‘“* Kelaart ” class of 
pearls was therefore probably due to a difference in their secondary 
growth, rather than in their primary origin. One of those 
sectioned (Preparation N. IV.) had a pseudo-nucleus composed of 
stratified columnar substance, with internally some nacre sur- 
rounding a small mass of brownish granules. 
It cannot, I think, be argued in comparing these pearls with 
‘eylon pearls that they are all seed-pearls or “ muscle-pearls.” 
They occurred in all the usual parts of the external body-wall and 
mantle, 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. Two Pearls from Margaritifera vulgaris /rom the Mediterranean, 
given to me by Professor Raphael Dubois. 
Professor Raphael Dubois most generously placed at my 
disposal for comparison two small pearls taken from J/. vulgaris 
from the coast of Tunis. This species has firmly established 
itself in several parts of the Mediterranean, since the opening of 
the Suez Canal, having no doubt come through from the Red Sea, 
either in the free-swimming 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, rather less than °5 mm, in 
diameter, which on being sectioned proved to be composed of very 
homogeneous granular matter surrounded on one side by 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 smal] amount 
of granular matter, surrounded by what looked like st ratified 
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 necessary 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 I have described above, for pearls from the 
same species from other localities. 
I. Pearls from M. vulgaris from New Caledonia, given 
to me by Professor Seurat. 
Professor L. G. Seurat, at my request, very kindly sent me four 
small seed-pearls from Margaritifera vulgaris, from New Caledonia, 
and also a slide, showing a larger pearl from the same species 
[85] 
