FOOD AND FEEDING IN FRESH-WATER MUSSELS. 
455 
passed slowly out of the stomach and accumulated in a mass about 1 millimeter 
long, which moved slowly along the intestine and was discharged in one mass into 
the mantle cavity at 11.30 a. m., about one hour from the time it had been ingested. 
The walls of the alimentary canal retained a pinkish coloration as if the epithelium 
had been stained by the carmine. In this observation a rotating mass of material 
could be seen in the loop of the intestine, consisting, no doubt, of particles kept in 
motion by the crystalline style. 
A specimen of Lampsilis luteola was observed while in a suspension of debris, 
particles of which passed to the palps, where some passed down the dark vertical 
streaks (the grooves) on the inner faces and some passed forward, usually fairly 
near the top of the palp, to the mouth. The larger share of particles passing off 
the palp went down the first two or three grooves, but a considerable number reached 
the middle or even the more anterior grooves before being carried down. This 
material on reaching the lower edge of the palps moved backward along the edge 
and merged with the heavier stream passing down the posterior two or three grooves. 
The posterior end of the palp as far forward as the posterior two or three grooves was 
often curled up somewhat. 
A specimen of Lampsilis luteola was allowed to ingest carmine until it became 
red from stomach to anus. In this, as in all the other cases, no considerable quan- 
tity of material accumulated in the stomach. The ciliary movement going on there, 
and perhaps the action of the style, kept the material passing on into the intestine 
fairly rapidly, so that the stomach was never packed full, as the intestine usually is. 
This mussel was fixed and sectioned, the sections being mounted unstained. In 
Figures 7 and 8 photomicrographs of sections of the stomach and intestine are 
shown. Particles of carmine were plainly visible in the stomach, and the lumen of 
the intestine was packed solidly with it. The epithelial cells of the alimentary canal 
had taken the stain sufficiently to give them a marked pink color. 
MUSSELS 12 MM. LONG. 
At this size the anatomy of the mussel is substantially that of the adult, except 
that the outer gill is still less than half its final width (fig. 6, p. 453) . For that reason 
it plays little or no r61e in feeding. 
Several specimens of Anodonta imhecillis were observed ingesting small particles 
of debris. This passed in at the inhalent siphon, fell upon the inner gill, passed 
down to its lower edge, went forward along it (probably a groove there) , and entered 
between the palps. Some particles moved forward across the upper part of the 
palp to the mouth and accumulated in boluses in the esophagus and were ingested. 
Other particles passed down the vertical grooves and were thrown off the palp, as 
previously described (fig. 6) . Sometimes the posterior end of the outer palp curled 
far upward. The inner palp could not be seen clearly in the living mussel, but in 
some of the sections the posterior end of the inner palp was curled around so it lay 
next to the visceral mass (fig. 13). Cobb (1918) found that both the attached and 
detached palp responded to stimuli by curling outward at its posterior tip. This 
would operate to stretch the inner surface of the palp, thus widening at least the 
posterior grooves and perhaps all of them. More material would fall into them and 
