382 REPORT 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 bringing them 
into ponds in which a large quantity of diatoms had been developed 
under favorable conditions. To accomplish this satisfactorily, however, 
a closer study of the life-history of this group would be necessary. 
The quantity of diatoms which 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 itis 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 ourrivers. 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 containeé 
in their stomachs the same species of diatoms as those collected around 
Newport News, or even around Hampton. 
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 power of discrimination between the higher and more active 
animals, such as copepods 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. 
Such a fact, however probable, 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 possess in general a 
power of discriminating between the different kinds of food offered to 
them? For this purpose it was 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 accomplish this. I 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 
which I employed to obtain cultures of a single species, only contami- 
nated by bacteria. The method was this: Some sea water was placed 
