255 



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 cur\e represented by the dotted line in the 

 graph (fig. 97) and is probably more t\'pical 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 



1 2 3 4 5 Ci 7 S 9 10 U 12 13 14 15 



Salinity in parts per 1000. 



Fig. 97. Activity of Teredo iiavalis in water of various salinities. 



only an approximation of actual conditions. 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 salinities of 

 15 and9 parts per 1000, 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 as great in a 



