FISHERY RESOURCES OF THE PHILIPPINE ISLANDS. 



97 



crab {Alphcus avarus Fabricius) which is ahiiost without exception 

 found living in pearl oysters as a commensal. 



Pearls may be found in any part of the oyster, or in the shell. The 

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

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

 calcospherules. The so-called "blisters" on the inside of the pearl shell 

 are usually produced by Ijoring worms or by some external injury. How- 

 ever, in one case at least, 

 a very fine blister now in my 

 possession was caused by a 

 small black pebble which 

 was completely embedded in 

 the shell. Blisters frequent- 

 ly contain pearls of value, 

 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 

 when broken, showed two 

 fine pearls, embedded and 

 hidden in the 

 (For similar ex- 

 amples see figs. 3 and 4.) 

 Cyst pearls are found in the mantle or soft parts of the oyster. These 

 are formed by a larva, usually a cestode, which enters some 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 

 Mr. Hornell ''^ that this pearl-secreting epithelium is of ectodermal origin. 



A bit of shell 



pesos was hidden, 



pearl was located, 



open, showing the 



pearl valued at 500 

 , flg. 3, shows where the comjuletely 

 is the same shell cracked gi^pii 



ARTIFICIAL PRODUCTION OF PEARLS. 



From the time of Linnceus, 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 Mussela by Action of Trematodes. 

 Froc. Zool. Soc. London (1902), 140. 



''Notes on Peail Formation in the Ceylon Pearl Oyster. Rep. Brit. Assoc. 

 (1903), 695. 



