382 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. 



of the life-history of the diatoms should be made. It does not seem to 

 me that it would be very difficult to fatten oysters by briugiug them 

 into i)ouds in which a large quantity' of diatoms had been developed 

 under favorable conditions. To acconii)lish {his satisfactorily, however, 

 a closer study of the life-history of this group would be necessary. 



The quantity of diatoms Avhich may be seen on a bottom near the 

 shore, for example, does not in the least furnish us with a basis for 

 measuring the amount of oyster food there present, as many of these 

 forms are firmly fixed to the bottom, and so, of course, are entirely use- 

 less for that purpose. Since it is well known that too much fresh water 

 kills the marine diatoms, a careful study of the influence of fresh water 

 upon them would be necessary in order to determine the most promising 

 places for oyster- culture in our rivers. My station last summer, so near 

 the mouth of the river, was not well fitted for this, but I was able to 

 show that oysters coming from 15 miles farther up the river contained 

 in their stomachs the same species of diatoms as those collected around 

 Newport Xews, or even around Hamilton. 



As the water surrounding the habitat of the oysters contained, 

 besides diatoms, a great number of copepods, it seems strange that 

 these were not found in the oysters' stomachs also, as the stream of 

 water ingested by the oysters was certainly strong enough to draw the 

 copepods into their mouth along with the other floating particles. 

 The idea naturally suggested itself that perhaps the oyster might 

 possess a x)ower of discrimination between the higher and more active 

 animals, such as coi)epods and the lower foraminifera, and especially 

 the diatoms, although the fact that its mouth is continuously open 

 does not favor this view. It was thus thought advisable to make some 

 experiments bearing upon this subject. As copepods were not to be 

 obtained easily in pure cultures, it was thought that a substitute- for 

 them might be found in finely hashed fish, or, better still, shrimps. It 

 might safely be assumed that if oysters should prove to be able to 

 discriminate between such a food material and diatoms the chances are 

 that they would still more readily distinguish the latter from the 

 actively swimming copepods, since the presence of these would be 

 more readily detected by their movements. 



Su(;h a fact, liowever i)robable, could not be demonstrated, but the 

 question which could and should be determined by this method was: 

 Do the oyster and the other bivalve mollusks j)ossess in general a 

 power of discriminating between the diiferent kinds of food offered to 

 them? For this i^urpose it Avas necessary to obtain, in the first place, 

 cultures of diatoms in which animal life was absent. Since diatoms 

 have never hitherto, so far as I am aware, been obtained in pure cul- 

 ture, some experiments had to be made to acconqflish this. 1 was able 

 to obtain very good cultures, though not pure ones; the latter not 

 being attempted. It seems to me that it would be easy by the method 

 whicii [ employed to obtain cultures of a single species, only ccmtami- 

 nated by bacteria. The method was this: Some sea water was placed 



