STUDIES ON BIOLOGY OF FRESHWATER MUSSELS. 221 



stomach and becoming white in the style sac, indicating a change 

 from one color to the other. 



Only one explanation of the above differences offers itself 

 namely the effect of bacteria. These, through a mass effect or 

 through the breaking down of the style substance itself, are prob- 

 ably responsible for the white color. Rice (I.e.) has shown that 

 the abundance of bacteria and of nitrates is here subject to pro- 

 found variation, on account of the periodic discharge from the 

 septic tank mentioned above. Whatever the cause of the white 

 color it might have been expected to be mingled with green from 

 the normal food brought down from above. That green is actu- 

 ally present in concealment is shown by the boiling of such styles 

 (p. 226). The white style pertains mostly to the creek. In the 

 lake a white style is observed only during low water in mussels 

 which have been feeding near the creek outlet. During freshets 

 and great dilution of the bacteria it does not occur even in the 

 creek. These observations may be taken as a further indication 

 of the direct dependence of the crystalline style upon the char- 

 acter of the food. 



(c) The Feeding of Infusions. 



Previously I had observed the renewal of the style and the 

 accumulation of material in the alimentary tract of animals fed 

 with hay infusions rich in ciliates (Allen, I.e.). The unmistak- 

 able finding of protozoan fragments in the stomach showed that 

 some such material is ingested, and I was satisfied that the style 

 renewal was due to their presence. The above nannoplankton 

 studies suggested that there might also be food value in the bac- 

 teria and flagellates which are present in such concentration in 

 infusions. The former experiments upon the feeding of infu- 

 sions were repeated with the same results. Again, white crystal- 

 line styles appeared (p. 220). However, in order to determine if 

 the bacteria and flagellates present may be responsible for the 

 style renewal an attempt was made to separate them from the 

 large ciliates. The above method for the separation of plankton 

 was applied here. It was possible, at any rate, to dispose of most 

 of the bacteria by washing. The process resulted in the death 

 of many ciliates due to crushing and to the change into fresher 



