456 
BULLETIN OF THE BUREAU OF FISHERIES. 
be carried downward. The crystalline style was seen to rotate in one specimen, 
clockwise, viewed from the anterior end. 
MUSSELS OVER 12 MM. LONG. 
A specimen of Lampsilis gracilis 18 mm. in length was placed in a watch glass 
of water containing various plankton forms and debris and observed with the aid of 
a binocular microscope for some time. The mussel kept a stream of water passing 
in at the incurrent siphon during nearly the whole period. Everything carried by 
the approaching current was swept in except particles so large that they caught 
against the short tentacles located upon each side of the siphon. Filaments of 
alg38, as Lyngbya or Spirogyra, four or five times as long as the width of the siphon, 
were carried in if brought up endwise. Such filaments were usually swept along in 
endwise fashion, just as a log is carried by the current in a river. Filaments that 
met the siphon more or less broadside were caught by the tentacles and held outside. 
Usually very shortly after particles of debris or filaments had lodged upon the ten- 
tacles the valves were closed suddenly thus forcing a jet of water out of the mantle 
cavity and blowing the material off the tentacles. The current of water usually 
began entering the mussel again after a short interval. The culture contained also 
the spherical algae, Pleodorina and Volvox, debris, and some nauplii and copepods. 
Pleodorina was carried in by the current, as were the filamentous algae when moving 
endwise. Some of the Volvox were too large to pass into the siphon. The nauplii, 
being active, swam out of the current and escaped, being swept into the mantle 
cavity. After the mussel had been feeding for a time, perhaps 15 minutes, a string 
of mucus began slowly to emerge from between the valves just beneath the inhalent 
siphon. This continued to appear slowly and in an almost continuous strand during 
the whole time that the mussel was siphoning a stream of water through its body. 
Upon examination the mucus was found to contain quantities of filaments of Lyng- 
bya and Spirogyra and some Pleodorina. In the light of other observations, quite 
evidently this mucus had been carried from the palps by ciliary action, bringing with 
it some, at least, of the material that had entered the inhalent siphon and which had 
failed for some reason to reach, or at least to enter, the mouth. 
During the observation some of the feces expelled from the exhalent siphon were 
examined and found to contain fragments of Pleodorina, diatoms, and a few pieces 
of filaments of Lyngbya and Spirogyra, showing that some of the Pleodorina were 
being ingested and that a few, at least, of the filaments of Lyngbya and Spirogyra 
had been brought up to the mouth in such a position that they could enter. 
A specimen of Lampsilis gracilis about 15 mm. long was placed in a culture 
similar to that just described. Even at this size the valves of this species are so 
thin that they are somewhat transparent, and the course taken by some of the larger 
particles after they had entered the mantle chamber could be observed with the aid 
of the binocular microscope and the electric light. The filaments of algae, being 
fairly large, could in many cases be observed during almost their entire course 
through the mantle cavity. Most of the filaments were whipped forward rapidly 
over the gills and could be seen to pass between the palps. Their movements at 
the anterior part of the palps and in the mouth region could not be observed, since 
