246 The Philippine Journal of Science i9i6 



throughout the Sulu Archipelago wherever the conditions are 

 favorable, provided that it has not been removed by human 

 agency. 



The life history of this mollusk is as follows: The female 

 gives off thousands of small ova, the male animal gives off 

 microscopic spermatozoa, and fertilization is left to the chance 

 meeting of these bodies in the water. When the egg is fer- 

 tilized, it becomes round and develops small cilia, which enable 

 it to swim about. It is doubtless carried many miles by currents 

 and tides. The shell begins to form at the end of the second 

 day, and after about eight days the young oyster settles and 

 attaches itself to whatever offers. The young oysters seldom 

 move far from the place where they first become attached, al- 

 though the old shells wear away the ropelike byssus and lie 

 free on the sea bottom. They continue to grow for perhaps 

 from ten to twelve years, although they are sexually mature 

 in two years and attain "legal" size, that is 14 centimeters, in 

 about three or four years. The rapidity of their growth depends 

 largely upon their location and the abundance of the microscopic 

 marine animals upon which they feed. 



For its proper growth the gold-lip pearl oyster requires a 

 warm, shallow sea, from 1 to 70 fathoms in depth, strong ocean 

 currents, and water with a specific gravity of about 1,02. The 

 bottom must be of sand or coarse gravel made up of dead coral 

 and broken shells. One of the most prolific bottoms examined 

 during my inspection was composed of what the diver called 

 "mud," which was in fact very fine, sandy ooze, consisting 

 chiefly of dead Foraminifera. This bed was covered with a 

 short growth of eelgrass. There are many places throughout 

 the Sulu Archipelago where these conditions exist, and the most 

 prolific pearl beds are found in such localities. 



LOCATION OF PEARL BEDS IN MINDANAO AND SULU 



Practically all of the area from Mindanao to Borneo is one 

 great pearl bed, yet the beds are more or less localized and 

 centered about various islands. Therefore I found it convenient 

 for the purpose of examination and reference to divide this 

 area into ten separate groups or pearl beds as follows (Plate I) : 



The Jolo pearl beds. — The Jolo beds include the following: 

 Jolo, Marongas, Pangasinan, Hegad, Bubuan, Minis, Cabucan, 

 Pantocounan, Bancungan, Tulayan, Capual, Bitinan, Dongdong, 

 Pata, Patian, and Teomabal Islands and the banks, shoals, and 

 islets in the immediate vicinity of these islands. The most 

 prolific sections of the Jolo pearl beds are the channels between 



