448 
BULLETIN OF THE BUREAU OF FISHERIES. 
One mussel finally became very active and moved about by means of the 
ciliated foot. Very fine particles of debris floating on the water could be seen to 
pass between the edges of the valves into the mantle chamber. The particles were 
for the most part extremely fine, best seen with the relatively low powers of the 
binocular by turning the substage mirror so that the particles caught the light and 
resembled dust motes in a sunbeam. They entered the mantle chamber in front 
of and at the sides of the foot, not in the siphonal region. Owing to the greater 
relative convexity of the shell, darker pigmentation of the tissues, and minuteness 
of the parts of these small mussels it was impossible to follow these particles after 
they entered the mantle chamber. No particles, however, except discharged 
feces, were seen to leave the mantle chamber, so it would appear that the material 
was ingested. Several small flagellates and ciliates were drawn near or approached 
the gaping valves but darted away before or upon touching them. In fact, most 
of them were too large to enter, even if they had been inert. 
On the next day one of this same lot of mussels (now about 36 hours off the 
fish) was observed for an hour or two. It steadily took into the mantle chamber 
fine particles in front of and at the sides of the foot. At times a black mass could 
be observed whirling about in the stomach. Later on, by observing somewhat 
larger mussels, this was ascertained to be a mass of ingested material and mucus 
being rotated by cilia on certain cells of the stomach wall. Powdered carmine was 
added to the culture. Considerable was drawn into the mantle chamber and soon 
a red mass could be seen whirling about in the stomach, showing that carmine had 
been ingested. (Nelson, 1920.) 
MUSSELS 0.28 MM. LONG. 
The anatomical features at this stage have not progressed much beyond those of 
the preceding. A specimen of Lampsilis luteola was observed as described above. 
Minute floating particles were being drawn between the valves at the anterior end 
and on the ventral side. Some very small flagellates were seen to pass in, but none 
could be observed to pass to the esophagus, all passing off the rudimentary palps. 
Powdered carmine was put in the culture and the currents ceased, though the 
valves remained gaping. No action was seen for 10 minutes, when the mussel was 
removed and placed in a culture free from carmine and the current soon began 
again. 
MUSSELS ABOUT 1 MM. LONG. 
At this stage the papillae of the inner gill have united at the ventral ends, pre- 
senting more the appearance of the adult structure. The outer gill is yet unde- 
veloped. The alimentary canal has about the shape shown in Figure 2. The 
siphons have not yet appeared. There are, however, two palps on each side, the 
apposing faces of each pair showing transverse ridges (fig. 9, opposite p. 458) . The 
ridges and the furrows are ciliated. When mussels of this size were lying or 
crawling upon a glass substratum with a relatively small amount of debris about 
them, the currents of material passed in at points all along the valves from the mid- 
ventral side to the anterior end, as was true of the smaller forms. An effort was 
