'.js; SEALE. 



LIFJi HISTORY 01' THE I'EAHL OYSTEII. 



The oysters are of separate sex, male and female. The eggs of the 

 female, when ripe, are extrudfd into the sea watei', where they are 

 fertilized by the spermatozoa of the male, if by chance the currents bring 

 the two elements together. Doctoj- Hornell ^ observed in regard to the 

 Ceylon pearl oyster, "that a ripe female, in close proximity to a mature 

 male, was sufficient cause lo excite the male to throw off spermatozoa." 

 The meeting of (lie spermatozoa and ova is left entirely to chance. 



The eggs of the Philippine pearl oyster (.V. maxima. Jamson) are at 

 first pyrifoim (see fig. 1) and float on the water; as soon as they are 



fertilized, they become round ; 

 and when from three to six 

 hours old, they move altout 

 by impairs of small, hair-like 



// \ \ \ Jt cilia. .'~!epiiiciitation is com- 

 / L/o\ \(^\V\K plete, but unequal. The shell 



" - -'''' ' '^ '' ' ' licgins to form at the end 



of the second day, and in 

 from four to eight days the 



Fig. 1. — Spermatozoa and ova of Philippine pearl 



oyster. young oystcrs settle and be- 



(«) Micropyle through which the spermatozoa (,Qj-,.|g attached tO the bottom, 

 enters the ova. i . , j i i 



(6) Nucleus. '-'1' to siiy object they chance 



(c) Nucleolus. to fall upon. At this stage 



id) Spermatozoa of male. jt i i i 



they are known as spat and 

 are about 1 millimeter (0.04 inch) in length. They attach by means 

 of a small tuft of coarse, hair-like bristles, known as the bvssus. 



Bach mature female contains several thousand eggs, but no doubt the 

 destruction of eggs and young is very great, many being swept into great 

 depths by strong currents, where they either perish or settle on the 

 bottom so thickly as to smother each other; or else they become covered 

 with sand, or attach to some floating object and are washed ashore. 

 Apparently, there is no fixed time in the Philippines for the maturing 

 of the ova, as sexually ripe individuals are found at all seasons of the 

 year. 



The shells are supposed to reach a maximum size and are most valuable 

 commercially in from four to five years, although they doubtless con- 

 tinue to grow for several years longer. I have examined specimens 

 weighing 5 kilos (11 pounds) which I believe were ten to twelve years old. 

 However, shells older tlian fi\e or six years arc apt to be worm-eaten 

 or full of holes caused by boring sponges, and so are of less value, ilore 



' Report on the operations of the Ceylon pearl banks during the fishery of 

 1905. Rep. Ceylon Murine Biol. Lai. (1906), 55. 



