128 SPOLIA ZEYLANICA. 



present when the ojjerations began. Dr. Pearson states that 

 it would appear that all the species of cestodes, obtained as a 

 result of the feeding experiment, were derived from the oyster. 

 In that case he admits the entire efficacy of the purgative. 

 Commenting on my statement that I believed it probable 

 that these cestodes {i.e., those other than the pearl-inducing 

 worm) were present when the fish were placed in the nursery, 

 and that the purgative employed failed to dislodge them. Dr. 

 Pearson states that if that was the case the value of the 

 experiment is entirely annulled. According to him, therefore, 

 the experiments are useless, and they also prove that four 

 species of larval cestodes inhabit the tissues of the oyster ! 



To advance the theory that all the adult cestodes obtamed 

 from the fish were derived from the oyster, is to brush aside 

 the obvious explanation, backed bj^ all available evidence, and 

 to substitute a less probable theory whose only support is its 

 ingenuity. If the larva of all these four species of cestodes 

 occur in the oyster, why was it that during one year only 

 T. herdmani was obtained, whilst the next year P. hutsoni 

 and P. kerkhami were obtamed, T. unionif actor being present 

 in both cases ? 



Currents. 



We stated that during our period of office we found no 

 evidence to support the conclusion that oysters were occasion- 

 ally silted over by sand. We gave this as being our actual 

 experience during the five years we held office. Dr. Pearson 

 states that our conclusions can hardly be regarded as con- 

 vincing. The mere expression of an opinion cannot alter the 

 actual experience we had. The extract from Captain Legge's 

 report, which Dr. Pearson quotes as being opposed to our 

 results, is of no consequence. According to this report, 

 places on which Captain Legge dived during March of a certain 

 year were then level rock with a coating of three inches of 

 sand. During November these sjiots were covered with 

 a foot of sand. There is not the faintest possibihty of the 

 spots on which Captain Legge dived in March being exactly the 

 same as those dived on in November. Again, it is stated that, 

 as the tanks submerged by Captain Donnan (covering perhaps 

 eight square yards of the ocean floor) on the Shoal Buoy 



