CRYSTALLINE STYLE OF LAMELLIBRANCHS 103 



Here the mechanism described above (p. 78) comes into play, 

 and by means of this most of the sand grains are separated from 

 the food particles and are carried into the intestinal groove, while 

 the latter pass out of the left side of the caecum. From here the 

 ciliary currents carry the food across the ventral wall of the 

 stomach to the right side of the gastric shield, where it again 

 enters the revolving alimentary mass (fig. 12). 



In the two mussels which I had under observation a steady 

 stream of sand and food particles was entering the right side of 

 the caecum, while a stream of practically pure food particles 

 was issuing from the left side. At the same time pellets com- 

 posed almost exclusively of sand grains were passing along the 

 intestinal groove and into the intestine. From time to time 

 small portions of the three streams just described were removed 

 and examined microscopically, and revealed the fact that prac- 

 tically complete separation of food and sand was taking place in 

 the caecum. 



By means of this mechanism the ingested material in the 

 stomach is gradually sorted over and purified, until, when feed- 

 ing has ceased, the stomach contains a mass of pure food 

 material. 



In all cases where I have had the revolving style under obser- 

 vation the motion is not continuous, but is interrupted by 

 periods of inactivity, preceded by a gradual slowing down of the 

 style. During these periods of cessation the cilia of the style 

 sac themselves become greatly reduced in activity. After a 

 period of rest the cilia again begin to beat actively, followed by a 

 resumption of motion of the style. What the stimuli may be 

 that cause the cessation and resumption of motion on the part 

 of the style I have been unable thus far to determine. The 

 presence or absence of food in the stomach itself seems to be of 

 no consequence so far as this activity is concerned. It is pos- 

 sible that the large bristle-like cilia of the style sac may be 

 under the control of the nervous system and respond to certain 

 internal reflex stimuli called forth by the stage of digestion of the 

 animal. 



