30 



8. Now what were the conditions during these months? 

 When I left Ennore on 23rd September, the backwater as it 

 had been for the } T ear preceding had no opening into the sea 

 and the rains had not commenced on the coast, although the 

 level of the backwater had shown signs of rising. A few days 

 after I left heavy rains were experienced and during October 

 the backwater rose rapidly and so high that to relieve the 

 pressure of the flood in the Buckingham Canal which crosses 

 the backwater, steps were taken by the Public Works Depart- 

 ment to cut a channel from the backwater to the sea. On 25th 

 October when the flood level had risen three feet above the 

 level at which it stood on 23rd September, the cut was made, 

 the head of flood water rushing through to the sea with such 

 violence that a deep channel was formed with the result that 

 from that date to the present the backwater has remained tidal. 

 This access of a great volume of fresh water poured into the 

 backwater during the three weeks preceding 25th October 

 very greatly reduced the density of the water and this taken 

 in conjunction with the fact that the October laying of spat- 

 collectors was the one marked by the best set of spat obtained is 

 strong evidence that this rapid reduction in the density of the 

 surrounding water was the stimulus requisite to stir the adult 

 oysters in the backwater into sexual activity — the emission of 

 milt or spermatozoa in the case of the male and of ova ready 

 for fertilization in the case of the female. A heightened 

 temperature certainly was not the cause, as the temperature 

 of the water before the onset of floods was higher than during 

 their continuance. 



9. The experiment, imperfect as it admittedly is — I was 

 absent during the whole time it was being conducted — proves 

 two points of the greatest interest : — (a) that the maximum 

 sexual activity of the edible oyster of the East Coast rivers and 

 backwaters synchronized with the heavy rains of October and 

 November^ October being apparently the optimum ; (b) the 

 exceedingly rapid rate of growth indicated for our Madras 

 oysters. It also furnishes very strong evidence in favour of 

 the view that a rapid reduction in the density of the surround- 

 ing water and not an increase of temperature as in European 

 and American waters, is the factor which determines the season 

 at which the majority of oysters shall spawn. 



10. With regard to the rate of growth of oysters; in 

 France the spat w 7 hich attaches to collectors, say in the first 

 week of July, is not detached till October, a period of at least 

 three months, and by this age it is not larger than the thumb 

 nail, at the outside 1-80 centimetre or about f inch in diameter. 



