STUDIES ON BIOLOGY OF FRESHWATER MUSSELS. 219 



smaller organisms. But when the matter of dilution or concen- 

 tration is taken into account, we have such an argument. The 

 greatly concentrated net-plankton was fed in a container of water 

 which was changed but slightly throughout the experiment. The 

 nannoplankton, on the other hand, was caused to stream over the 

 second group of mussels in the original water, and with the orig- 

 inal concentration. If it had been concentrated as much as the 

 net plankton a much more marked ingestion would probably have 

 been obtained. It is hoped that in the future a method for con- 

 centrating nannoplankton in quantity may be applied to the solu- 

 tion of this question. 



An experiment similar to the foregoing consisted in placing 

 starved mussels in the creek, enclosed in a tight metal container, 

 whose two ends were then closed with bolting-silk. The creek 

 was dammed on either side of the container, so as to raise the 

 level slightly and maintain a flow of water through it upon the 

 mussels. The stopping of the meshes of the silk was expected to 

 interfere with the flow after a few hours. But, as a matter of 

 fact, there was sufficient eddy and overflow to keep the silk fairly 

 well washed, so that at the end of the experiment a slight current 

 might still be detected. 



Experimental mussels and checks were placed both above and 

 below the sewer outlet, where they were allowed to feed for 

 twenty-four hours. Small numbers were used here four mus- 

 sels in each situation. So far as the results derived are trust- 

 worthy, they show a utilization of nannoplankton as food, and 

 corroborate those of the previous experiment. 



The mussels from the three situations showed a well-defined 

 gradation in the reconstruction of the crystalline style: (i) those 

 from experimental conditions showed only a partial renewal; (2) 

 the checks nearby had virtually completed the renewal; (3) 

 below the sewer outlet the checks had well formed and entirely 

 hyaline crystalline styles. Presumably they had an additional 

 source of food the sewer. 



The mussels used as a check, and whose styles had grown 

 large and hyaline, accumulated considerable masses of green in 

 the intestine during the twenty-four hours. Examination showed 

 this material to comprise, among other forms, Namcula, Oscil- 



