FISHERY RESOURCES OF THE PHILIPPINE ISLANDS. 97 



crab (Alpliciis avaiitt! Fabricius)' which is almost without t'xi.iq^tion 

 found living in pearl OAsters as a commensal. 



Pearls ma}- be found in any part of the oyster, or in tlie shell. The 

 free pearls and those atiaelied to the shell result from some injury, while 

 those in the mubdes are formed around small, calcareous bodies called 

 caleospherules. The so-called "blislers" on the inside of the })earl shell 

 aie usually produced by boring worms or by some external injury. .Flow- 

 ever, in one case at least, 

 ■■irr-'- a very fine blister now in niv 



possession was caused by a 

 _^ small black pebble which 



was completely embedded in 

 , ;ji-^ the sliell. Blisters frequent- 



ly contain pearls of value, 



Fig. :-i. . 



and specimens of good shape 



'** ,,^ and luster may become fully 



--'^'' ''■■ ,' embedded in the shell. I 



now have a shell before me 

 •. " ' "~ which, when found, exhib- 



~ - — ' ited no sign of a pearl, but 



FIG. 4. wlien broken, showed two 



A bit of sheU in which a pearl valued at 500 '^1^2 pearls, embedded and 

 pesos was hidden. The X , fig. 3, shows where the complctelv hidden in the 

 pearl was located. Fig. 4 is the same shell cracked in /-r^ • n 



.... , shell. (For Similar ex- 



open, showing the pearl. ^ 



amples see figs. 3 and 4.) 

 ( 'yst pearls are found in the mantle or sqft parts of the oyster. These 

 are formed by a larva, usually a cestode, which enters so.me portion of 

 the connective tissue where, as stated by Doctor Jamson,^^ it at first 

 occupies a space lined with connective tissue fiber ; but the oyster soon 

 gives rise to a pearl-secreting, epithelial layer which lines this space and 

 becomes the pearl sac, I am of the opinion held by Mr. Herdman and 

 ]\Ir. Hornell ^^ that this pearl-secreting epithelium is of ectodermal origin. 



AETIFIOIAL PEODUOTIOlSr OF PEAELS. 



From the time of Linnajus, who claimed to have discovered a method 

 whereby the oyster could be made to produce pearls, up to the present 

 date, the attempt to force the passive oyster into producing culture pearls 

 has never ceased, so that almost each year some one announces in the 

 press of the country that he has at last reached the true solution of the 

 problem and can produce pearls at will. There is no question but that, 



^' The Formation of Pearls in European Mussels by Action of Trematodes. 

 Froc. Zool. 8oc. London (1902), 140. 



"Notes on Pearl Formation in the Ceylon Pearl Oyster. Rep. Brit, Assoc. 

 (1903), 69.5. 



