114 CEYLON PEARL OYSTER REPORT. 



prosperity probably none are wholly without influence for good or evil, so closely 

 interwoven in past history and present function is the web of living nature. 



III. EEPBODUCTION AND LIFE-HISTORY OF THE PEARL OYSTER. 



We find that the Ceylon pearl oyster is dioecious, or has the sexes separate, not 

 only at any one period, but throughout the life of the animal. Our observations on 

 innumerable microscopic sections of preserved material, and Mr. HORNELL'S experi- 

 ments at Galle (see Part L, p. 125), have shown that quite definitely ; and there are 

 no traces of hermaphroditism. Emission of the generative products takes place 

 directly into the surrounding water, where the ova are fertilised, and consequently 

 there is no retention of eggs or embryos within the body of the female. The male is 

 stimulated to emit spermatozoa by the presence of ova in the surrounding water, 

 and as the animals are gregarious, and males and females are found mature together, 

 it becomes practically certain that all eggs will be fertilised under normal conditions. 



There is no marked disproportion in numbers between the sexes ; out of a couple 

 of hundred collected together at random and examined in 1902, 87 were males, 71 

 females, and the remainder immature or indeterminate. Similar observations made 

 on several occasions since have given us much the same results. 



Reproduction appears to take place to some extent throughout the year, and stray 

 individuals may be found to be sexually ripe in any month ; but there are two maxima 

 when the majority of the pearl oysters in the Gulf of Manaar become mature and 

 shed their reproductive elements, viz., in mid-summer from May to July and in mid- 

 winter from November to January. It must be remembered that the temperature 

 and other conditions in these two periods of the year do not differ very greatly. The 

 one period is during the prevalence of the south-west monsoon and the other during 

 the north-east. Hence the importance of ascertaining precisely the resulting currents 

 that would carry floating embryos as the result of the prevailing winds at each 

 such period is obvious. It will be noted that these statements are only made in 

 regard to the pearl oyster in the Gulf of Manaar. It may well be that even the 

 same species in other localities, such as the Persian Gulf or the Bed Sea, has other 

 breeding habits. 



Larval development takes place in the surface waters of the sea, and from our 

 observations we draw the conclusion that the young animal may settle down as 

 " spat " within 5 days of the fertilisation of the egg. At the same time, from the size 

 of some of the larvae we have found, we consider it probable that the free-swimming 

 period may on occasions be considerably prolonged. We were able to rear young 

 larval stages in the Galle Marine Biological Station, and we caught the later ones in 

 the tow-nets on the pearl banks. We found the youngest fixed spat on Zoophytes 

 and Algae early in November and early in March. All fixed stages, from one similar to 

 the latest of the free stages up to young oysters having the adult characteristics of 



