FOOD AND FEEDING IN FRESH-WATER MUSSELS. 
451 
This statement applies, of course, only to observations made with the mussel lying 
on its side on a substratum of glass with usually only a moderate amount of debris 
about it. 
Two specimens of Lampsilis luteola were removed from a rearing trough and 
observed at once in a culture of the material taken directly from the trough. A 
current of the fine debris in the water was, passing in and between the palps. Much 
of this passed downward and off the palps, but at the identical time some particles 
moved forward between the palps and up the esophagus. These particles passed 
between the palps rather near the upper edges. It could not be seen that they 
differed from those particles passing off the gills. It merely appeared that some 
of the debris moved across the inner faces of the palps to the mouth while some 
moved down and off. Both processes were continuing simultaneously. A specimen 
of Lampsilis luteola of this size also ingested carmine grains. The experiment 
was continued until carmine grains were observed in the feces. 
A specimen of Lampsilis luteola was placed in a culture containing red Euglenas 
160 by 35 micra in size. Some of the Euglenas were ingested, notwithstanding 
their size. They were apt to assume an approximate spherical shape when being 
moved in the ciliary currents. In the bright light reflected from the electric bulb 
up through the mussel red Euglenas were quite conspicuous and could be seen to 
fall upon the gills and pass down, some falling into the mantle chamber and some 
passing forward and between the palps. Of these latter some were thrown off and 
some taken forward to the mouth and up the esophagus to the stomach. In the 
stomach they were seen as a dark mass, rotating clockwise (viewed from anterior 
end of the mussel). The Euglenas were whirled about by this and batted, so to 
speak, into the caeca of the stomach at the sides and below the entrance from the 
esophagus. 
This specimen was fixed and sectioned and a photomicrograph of a section 
through the stomach is shown in Figure 5. Portions of the Euglenas can be seen, 
also tufts of long cilia on the sides of the stomach and a cross section of the style, 
which evidently projects into the stomach, as shown by Nelson (1918) for adult 
mussels. The style is kept in rotation by the cilia, and it is the movement of the 
two that causes the ingested food to be whirled about in the stomach as observed 
in mussels whose valves are sufficiently transparent to allow this movement to be 
seen. In view of Nelson’s (1918) excellent work on the crystalline style and the 
fact that the style was not the especial object of this study, no further suggestion 
will be made here concerning its function. 
A specimen of Lampsilis luteola was observed while in a culture containing 
some of the diatom Stephanodiscus. Some of these were ingested and could be 
followed as they passed from gill to palps and between these to the stomach. At the 
same time other specimens of Stephanodiscus were being carried down to the lower 
edges of the palps and thrown off. One or two ciliates larger than the diatoms were 
also observed during their entire course to the stomach. Their route was that already 
described. A considerable mass of debris was pushed with a fine glass rod up about 
the mussel as it lay on its side. Many particles were drawn in all along the edges 
of the valves from the anterior to the posterior end. Great numbers of these passed 
between the palps but were carried to the lower edges and thrown off. No atten- 
