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University of California Publications in Zoology [Vol.22 



above, boring was found to be very active, in 6 parts per 1000 slightly 

 less, in 5 parts per 1000 very rare, while in 4 parts per 1000 it was 

 never observed in the aquaria. 



There was also an accompanying change in the sensitivity of the 

 siphons, these retracting rapidly in the salinities of 6 and 7 parts per 

 1000. moderately in 5 parts per 1000, and slowly in 4 parts per 1000. 



Salinity in parts per 1000. 



Fig. 3. Graph representing length to which siphons of Teredo navalis 

 are extended in water of various salinities. 



Again, there was a marked change in the length to which the 

 siphons were extended, which is illustrated in figure 3. This curve 

 shows a gradual decrease in the length of siphons, with decrease in 

 salinity, the decrease per part per 1000 becoming greater as the 

 salinity decreases. 



The lethal salinity. — These observations indicate a general inter- 

 ruption of function in salinities below 6 parts per 1000, while below 



