354 University of California Publications in Zoology [Vol.22 



aquaria were used in determining the average per cent of siphons 

 extended by the teredos for each salinity tested. The number of 

 siphons extended from each specimen block was recorded each day for 

 a period of days after an apparent maximum had been reached which 

 did not fluctuate markedly. Low records during this period, accom- 

 panied by unfavorable aquarium conditions, were discarded. These 

 values were averaged for each specimen and the per cent of siphons 

 extended was computed by comparison with the number of siphons 

 originally extended from the same block in 15 parts per 1000 salinity. 

 The average per cent for each salinity was computed from the average 

 of the ten specimens. The per cent of siphons extended in 3 parts per 

 1000 salinity was determined separately under similar conditions, but 

 during a shorter period of exposure. 



The percentage of siphons extended from control blocks exposed 

 during the experiment to a salinity of 15 parts per 1000 — which should 

 obviously be 100 per cent — was found to be only 92 per cent of that 

 in earlier tests. If we assume that 8 per cent of the individuals were 

 killed off by the conditions of life in the aquaria, we may raise all 

 the values 8 per cent. This produces a curve represented by the 

 dotted line in the graph (fig. 2) and is probably more typical than 

 the curve obtained from the actual values computed from the records 

 of the experiment without this correction. 



The individual values from which the percentages for the curve 

 were computed show deviation of 15 per cent from the mean in some 

 cases, and at best the curve is only an approximation of actual con- 

 ditions. Had it been possible to use a salinity nearer the optimum 

 for the organism (probably about 20 parts per 1000) in determining 

 the 100 per cent value for the graph, the position of the curve would 

 have been changed to some extent. The decrease in per cent of 

 siphons extended, between 15 and 9 parts per 1000 salinity, is very 

 slight, however, and it may be expected that the increase between the 

 salinity of 15 parts per 1000 and the optimum will be correspondingly 

 small. None of these deviations will greatly alter the shape or position 

 of the curve. 



The curve indicates that the activity of the borers is nearly or 

 quite :is great in a salinity of 9 parts per 1000 as in higher salinities. 

 In salinities below 9 parts per 1000, the per cent of functioning 

 individuals becomes less, and decreases more rapidly as the salinity 

 is decreased, until at 3 parts per 1000 there are no siphons extended. 

 The curve descends rather gradually from 9 to 6 parts per 1000 and 



