WINDOW-PANE OYSTER INVESTIGATIONS. 139 



A sketch map is annexed showing the distributions of 1912 

 oysters by horizontal Hnes, and that of this year's oysters by 

 vertical lines. It also indicates the areas mentioned in this 

 Paper. A diagram is also given which compares the sizes of 

 first-year oysters in May, 1912, with first-year oysters in Maj^, 

 1913, the measurements of the short diameter being given. 



Note by J. Pearson. 



Mr. Hemy's report of January and May inspections shows 

 once more how critical is the rainy season of the north-east 

 monsoon. In January, 1912, a fairly large bed of oysters was 

 practically wiped out as the result of the heavy rains in the 

 previous November and December. In the inspection of May, 

 1912, a very large bed of young oysters was discovered. 

 These have also been destroyed hy the excessive rains of 

 January, 1913. As a rule January is a dry month. The 

 oysters had evidently survived the November and December 

 rains, and it is unfortunate that the rains in January were so 

 abnormally heavy. It may be presumed that oysters which 

 survive the first rainy season are not so much affected by the 

 second, and if the large bed of oysters could only have 

 survived, a lucrative fishery would have resulted in two or 

 three years' time. 



It seems highly probable that Placuna spawns when only 

 twelve months old, and the evidence collected during the 

 last two years renders this almost certain. Although we have 

 not yet been able to discover the larvae in the plankton, we 

 can be certain that spawning does not take place until after 

 the rains. If the larvae were hberated before or during the 

 rains they would be killed. For the last two years we have 

 had large spat-falls after exceptionally wet seasons. We are 

 thus forced to the conclusion that spawning follows the rains. 

 In fact it is probable that the low salinity of the water stimulates 

 the reproductive organs. ]\Ir. Henry shows that the young 

 oysters found this jea.r are smaller than those recorded last 

 year. This is probably due to the fact that the rains were 



