December 15, 1916] 



SCIENCE 



853 



many that the oystermen had almost entirely 

 -abandoned the field, and sought other occupa- 

 tion. This fact was completely established. 

 Professor Grave admits an " unusually large " 

 death rate, adding that the " planters readily 

 imagined that the poor condition and death 

 of their oysters were in some way causally 

 connected with this sediment in the water." 

 Commissioners, then referees, and finally a 

 jury, readily imagined the same thing, and 

 awarded them damages for their losses. Why 

 should Professor Grave's oysters have thrived 

 while those of the oystermen died? 



It is not without interest that the death of 

 .the planted oysters, and other lamellibranchs 

 on the same ground, could not be accounted 

 for by the presence of starfish, drills or other 

 enemies, or from any disease. On the other 

 hand, Professor Grave's oysters may have sur- 

 vived for two weeks, and added a " perceptible 

 growth" to the shell for several possible rea- 

 sons. 



A few of the bed oysters had lived, not two 

 weeks, but two years or more after dredging 

 had begun. A good many survivors were found 

 behind a bar that deflected one of the two 

 main flood currents away from them. The 

 accident of position may have been favorable 

 to Professor Grave's oysters, but they would 

 have lived much longer than two weeks any- 

 where on the beds. 



During the summer of 1911, when this ex- 

 periment was made, dredging was intermittent. 

 Frequently so little of it was being done that 

 the flood tides bore comparatively little sedi- 

 ment over the beds. 



Again, at the time of this experiment most 

 of the dredging was being done at a much 

 greater distance from the beds than formerly, 

 and the water was proved to bear very much 

 less silt than in 1909 and 1910 when the mor- 

 tality on the beds had been greatest. This fact 

 alone should be sufficient to explain Professor 

 Grave's result. 



That oysters in good condition, "gathered 

 from a bed far removed from the scene of 

 the dredging operations," should fail in 

 two weeks to become emaciated — or should 

 thrive — was to be expected. Nor, considering 



the possible conditions, was I surprised at Pro- 

 fessor Grave's results in his examination of 

 the contents of their stomachs. I was not 

 able to see that the fact that his oysters fed 

 " in waters that were turbid with sediment " 

 was at all in opposition to my conclusion. 

 " Turbid with sediment " is a relative — a very 

 indefinite — term. I believe that any lamelli- 

 branch is able to take into its stomach any 

 suspended particles, sand grains as well as 

 diatoms, even in turbid water, until a definite 

 point is reached at which they become too 

 numerous, and that then they are all carried 

 out of the body. It is unfortunate that in 

 my work on the ciliary mechanisms I have not 

 determined precisely how turbid the water 

 must be, that is, how large a proportion of sus- 

 pended matter must be present, to bring the 

 discharging mechanism into action; but in my 

 experiments there was always such a point. 

 Professor Grave asserts his disbelief even in 

 the existence of a normal mechanism of this 

 kind as I have described it, though I have no 

 reason to think that he ever took the trouble 

 to look for it. I am not particularly anxious 

 over final judgment on that matter, or on the 

 "Kellogg theory" of its operation. 



The most interesting of Professor Grave's 

 assumptions, however, concern food selection, 

 and my statement that the beat of cilia is no- 

 where reversed. He contends that cilia of 

 " certain tracts " of the palps are capable of 

 being reversed, as in the case of the oyster, 

 " resulting perhaps from their stimulation 

 directly or indirectly by food particles," and 

 that this " may be the mechanism by which the 

 selection is effected." 



One is a little puzzled to understand, from 

 the statement of it, what is the mechanism and 

 its operation according to the Grave theory. 

 Does the reversal of cilia from stimulation by 

 food particles cause the rejection of food par- 

 ticles? If so, to what purpose? Or does 

 stimulation by food cause the rejection of 

 sand, and not of food particles? That would 

 be interesting. Professor Grave's theory cred- 

 its the oyster with the possession of a delicate 

 sense of taste, and he is rather scornful be- 

 cause mine does not. Does the taste of sand, 



