260 



explained by such a process. The above observation is more readily explained on the 

 basis of diffusion, as the speed of this process would be increased by motion and change 

 of water. The following experiment shows some results obtained with specimens in 

 running water. 



A series of aquaria was arranged so that currents of fresh water of three different 

 rates of flow could be passed through them. The rates of flow were not accurately 

 measured, but had the following relation; A>B>C. A was the discharge of a three- 

 quarter inch pipe, C a flow of approximately fi\'e gallons per hour, and B intermediate 

 between these currents. Specimen blocks containing teredos were exposed in these 

 aquaria and in aquaria containing standing fresh water. Two other specimens were 

 prepared from ordinary specimen blocks by co\ ering the split surfaces and cut ends of 

 the block with a thin coating of paraffin. These specimens were exposed simultane- 

 ously with the untreated specimens in aquaria through which currents B and C were 

 passing. All the specimens contained approximately the same number of live teredos 

 at the beginning of the run. After seven days the specimens were changed to water 

 of 15 parts per 1000 salinity. Table 40 gives the approximate number of individuals 

 surviving under the various conditions. 



TABLE No. 40 

 SURVIVAL OF TEREDO NAVALIS IN RUNNING AND STANDING FRESH WATER 



Table 40 shows that the survival was greater in standing water than in running 

 water, and greater in slowly running water than in swiftly running water. Specimens 

 having the cut surfaces protected by a coating of paraftin, and therefore having less 

 surface exposed for diffusion of water, show a greater survival than untreated speci- 

 mens. The explanation of the dilution of the water in the burrow by a process of 

 diffusion through the wood accounts for the above results, since the rate of diffusion 

 would be expected to increase with the rate of flow of the current. This would shorten 

 the time necessary for dilution of the water in the burrow, a condition which would 

 be followed by the death of the teredos. The speed of such a process would also be 

 decreased by reduction of the surface of the specimen by covering the cut surfaces 

 with paraffin. 



Table 38 shows that teredos lived longer in specimen blocks in water of 2 parts 

 per 1000 salinity than in zero salinity. This may be due to the fact that diffusion takes 

 place less rapidly between solutions nearer the same concentration than between solu- 



