REMARKS ON DR. PEARSON's REVIEW. 131 



large measure it is produced by the spin of the earth on 

 its axis. 



With reference to (ii.), it would be strange if, after five and a 

 half 3^ears of mtermittent work out at sea, ably assisted by a 

 Lieutenant in the Eojal Naval Reserve, we both failed to 

 reahze the difference between an oceanic current and a surface 

 drift. It is true that at any given time, and at any given 

 place, it is well-nigh impossible to state whether an obvious 

 surface movement is due to an oceanic current, or whether 

 it is merely surface cli-ift caused by the wind. Circumstantial 

 evidence would afford very valuable clues. In the time at our 

 disposal it was utterly impossible to attempt the differentiation 

 by means of water analyses. We shall wait with interest to see 

 what progress is achieved in this line during the next ten years. 



With reference to (iii.), w^e have alread}^ pointed out in this 

 Paper, and in our Report (Part VI., page 235), that duruig a 

 weak south-west monsoon no currents are present on the 

 plateau which was under lease, and that the northerly set is 

 entirely a surface drift produced by the prevailing wind. 



Bearing of Drift Bottle Experiment. 



Dr. Pearson's statement on page 218, that we have failed 

 to realize that during the north-east monsoon spat may be 

 carried from the Cejdon banks to the Tuticorin banks, is 

 dependent on the supposition that oysters spaMU in December 

 to February. 



With reference to the spatting maximum, which is supposed 

 to take place dm'ing the north-east monsoon, Dr. Pearson's 

 conclusions are based on a short statement to this effect made 

 by Hornell. The phenomenon has never been noticed by any 

 other worker in the whole history of the pearl banks. As 

 the results obtained by Hornell are so often stated by Dr. Pear- 

 son to be in error, it is curious that this remark of Hornell's 

 should have been given such undue prominence. As it has 

 yet to be established that there are two spawning maxima, 

 there is little point in discussmg improbabilities. If two 

 spa\\Tiing maxima really exist, this mollusc will differ remark- 

 ably from Placuna and from most other molluscs, both in 

 Indian and home waters, whose habits are loiown. Over 300 

 samples of plankton, collected over four j^ears, during the 



