1922] Blum: On the Effect of Low Salinity on Teredo Navalis 357 



4 parts per 1000 there is little or no activity. We may expect that 

 above this critical range (4 to 6 parts per 1000) the teredos are able 

 to continue to live and function as regards salinity, while below this 

 range the organisms will die if exposed long enough. The salinity 

 below which the average individuals are unable to live may be called 

 the lethal salinity. This salinity has been more accurately placed at 



5 parts per 1000 by the following experiments. 



Teredos were exposed by splitting away the outer surface of the 

 specimen blocks and breaking away the thin shell around the pallets, 

 so that the animals were unable to plug themselves up in their 

 burrows. Individuals exposed in this manner lived for eleven days in 

 slowly running water of 5 parts per 1000 salinity, after which time 

 the results were obscured by fouling of the aquaria. The activity of 

 these teredos as manifested by the sensitivity of the siphons at the 

 end of this time was equal to that of specimens in 6 and 15 parts per 

 1000 salinity, as is shown in table 1. 



TABLE 1 

 Activity of Teredo navalis, Experimentally Exposed, in Various Salinities 



Individuals exposed to salinities below the lethal (5 parts per 

 1000) were killed off very rapidly, as is shown in table 2. The 

 criterion of death used in these experiments was the first appearance 

 of degeneration of the tips of the siphons. As soon as this degenera- 

 tion appeared, the specimen blocks were changed to water of 15 parts 

 per 1000 salinity, but the animals never revived after this degenera- 

 tion had begun. 



