STUDIES ON BIOLOGY OF FRESHWATER MUSSELS. 217 



intestines of mussels feeding in the escaping water. One com- 

 plete experiment follows : 



Water from the creek or lake was first poured through a cop- 

 per gauze in order to remove such debris as plant fragments and 

 flakes of limy incrustation. From these it passed into a conical 

 plankton-net of No. 20 bolting-silk, terminating in a detachable 

 Birge bucket. The lower portion of the cone and the bucket 

 were suspended in a jar of water. Measured quantities of the 

 natural water, varying from 50 to 250 liters in the several ex- 

 periments, were passed through. From time to time the meshes 

 of the bucket became choked and the process was slowed down. 

 This was especially true in the lake following high winds, when 

 there was considerable turbidity. At intervals, therefore, the 

 bucket was removed, rinsed out into a container, and the gross 

 filtrate brought into contact with a group of mussels which had 

 been starved for a few days in order to cause the disappearance 

 of the crystalline style. The overflow water which had passed 

 through the silk was allowed to siphon over into another jar in 

 which were kept another group of starved mussels. They were 

 thus given opportunity to feed upon nannoplankton almost solely. 



In order to demonstrate that any regeneration of the crystal- 

 line style that might occur could not be ascribed to the chemical 

 or physical character of the water itself, a quantity of the strained 

 water was also siphoned over into a sheet of filter paper and mus- 

 sels placed in the jar beneath. The mussels fed upon filtered 

 water in no instance showed the least evidence of re-forming the 

 style. That many organisms passed through the plankton net is 

 well shown by the amber-green coating which soon formed on 

 the filter paper. Upon these organisms the second group of mus- 

 sels had opportunity to feed, provided the gills might be a suffi- 

 ciently effective mechanism to entrap particles which had passed 

 through the silk. 



During the progress of the experiment, usually about four 

 hours, checks were kept in the lake or creek, near the experi- 

 ment. They also had been starved for the same length of time, in 

 tap water. 



The water was taken from a depth of two to three feet in the 

 lake, along the east shore, where it is open to wind and wave 



