siphons is resumed, provided the salinity is high enough or the respira- 

 tory need great enough to stimulate its resumption. 



The lethal action upon Teredo of brackish or fresh water is thus a 

 function of two variables, the salinity (or lack of it) and the length of 

 time between recurring periods of higher salinities which permit re- 

 sumption of more normal functioning. A Teredo might be able to 

 survive completely in repeated exposure to fresh water, provided sea 

 water of sufficient saline content was available between times. A sep- 

 aration of the relative action of these two factors can be made only by 

 carefully controlled experiments. Both factors operate continuously in 

 Carquinez Strait owing to tidal changes. 



It is obvious from the above consideration that mean salinities do 

 not fully reveal the lethal factors or their operation. These are best 

 revealed by the minimum salinities on the one hand and on th\e other 

 by the length of the intervals between recurring spring and midtides 

 of the month or other fluctuations which permit a sufficient restoration 

 of normal respiration and feeding to continue the life of the borer. 

 The survival of Teredo for 9 days in fresh water suggests an approxi- 

 mate adaptation to survival from the spring to the middle and vice 

 versa. From the records of the Dutch investigators of pile worms it 

 has appeared that a minimum salinity of 9 parts of salt per 1000 per- 

 mits the occurrence of Teredo. Our records indicate that Teredo sur- 

 vived here in the winter of 1920-21 in salanities which were much lower 

 than this, at least for much of the time from December to April. The 

 mean salinity at Crockett at the surface at low tide from November 19, 

 1920, to April 30, 1921, was 2.76. At high tide, it was probably 2.5 to 5 

 parts higher. Teredo survived near the surface in approximately these 

 conditions at Carq-uinez Strait Light, one mile below Crockett, and at 

 the bottom, up to within 14 feet of the surface, at Crockett itself. 



We have available this year continuous records of salinities at sur- 

 face and bottom at high and low tides, at Port Costa three times per 

 week, and daily at Martinez, but records only at the surface at low tide 

 daily at Crockett. 



These salinities are analyzed in the accompanying tables, with ref- 

 erence to the total number of days, from November 19, 1920, to April 

 30, 1921, the flood period of lowest salinities above and below each of 

 the parts per 1000" of salt from 1 to 15, at the bottom at high tide at 

 Port Costa, 2.5 miles above Crockett, and at Martinez, 5 miles above. 

 Bottom waters at high tide exhibit the maximum available salinities 

 most favorable to Teredo. The number of days of recurrent periods of 

 salinity at or above each of the parts per 1000, and the average and the 

 maximum days of lower salinities, between these periods, are also 

 tabulated. The number of periods and total number of days of given 

 salinities (or above) represent opportunities for nore normal respira- 

 tion and feeding. The number of days below represent less favorable 



