29 



tubes and crusting calcareous polyzoa, also two young Mytilus 

 •4 and -5 centimetre in length, respectively. On B were 3 

 Anomia averaging 2*25 centimetres diameter. Barnacles on this 

 tile were very scarce and quite tiny, but crusting polyzoa 

 was abundant and had interfered with the growth of several of 

 the smaller oyster spat. 



On A the whole of the 60 spat were located on the concave 

 side of the tile ; in B out of the total 58, 43 were on the 

 concave side, 15 on the convex. No observable growth of 

 algas had occurred on either tile, but the concave surface in 

 both had a somewhat dirty appearance due to the roughness of 

 the surface caused by the crowding and distortion of the young 

 oysters. 



Lots 6, 7, 8 and 9 — bih to 26^ November. — On none of 

 these was there any considerable set of spat. A typical tile 

 selected at random gave the following census : — 



24 on the concave side, 9 on the convex. Of the former, 

 the largest was 1-90 X 1*90 centimetre ; the smallest 0-65 X 

 0-60 centimetre. Between these extremes there was a perfect 

 gradation. Of barnacles there were 22 of about *3 centimetre 

 across ; no serpulids and no Anomice, but of crusting polyzoa 

 there. were three colonies, the largest being 3 centimetres in 

 diameter. 



Lots 10 and 11 of Zrd and 8th December appeared perfectly 

 clean and were put back into position again. 



7. Summarizing the results, it appears that spawning did 

 not take place till the very end of September or the beginning 

 of October, as the collectors put out on 23rd September bore 

 only a few odd spat of quite small size ; those tiles apparently 

 became fouled before spawning took place, and only recently 

 became scoured clean here and there, allowing of the attach- 

 ment of an occasional larva. 



The great number of spat of more or less the same age on. 

 the collectors laid out in October point to this month marking 

 the maximum or rather the optimum of the spawning activities 

 of the adult oysters in this locality ; alongside of the density 

 of set in October, we see a diminished set continuing until 

 December as shown by lots 6 to 9 laid down in November. 

 In this connection it must be noted that in this particular Indian 

 species as in the American O. viryinica, the ova pass several 

 days in a swimming stage before sinking to the bottom and 

 making attachment. Any that attached for instance on 25th 

 October were spawned probably about 20th October and so with 

 all other attachments. 



