362 University of California Publications in Zoology [Vol.22 



difference of concentration. Thus the dilution of the water in the 

 burrow would take place more slowly when the blocks were sur- 

 rounded by water of 2 parts per 1000 salinity than when surrounded 

 by zero salinity and the teredos would survive for a longer period. 



Teredos in the piles at Crockett have survived a greater period 

 of low salinity during the past season than have the teredos under 

 any conditions of low salinity in the aquaria (see tables 3 and 6). 

 The short period of survival in the latter case may be due, however. 

 to the greater relative surface exposed for diffusion in the specimen 

 blocks than in piles. Besides having their cut surfaces exposed in 

 most cases, these blocks were scrubbed free of barnacles and other 

 marine growths which cover the exterior of all piles. Thus there was 

 a relatively large surface exposed for diffusion, including the face of 

 the block, the split surfaces, the open ducts of the wood at the cut 

 ends, and the very large surface exposed by the opening up of many 

 burrows in cutting the block. As is shown in table 5, more toredos 

 survived low salinities when the cut surfaces of the blocks were 

 covered with paraffin although this covering did not adhere closely 

 in some places and was thus an imperfect seal. There must also be 

 a slight leakage through the pallets although they fit tightly and form 

 a very effective plug. 



At times during the period of low salinity at Crockett, when 

 several piles were pulled at the same time from the same locality it 

 was found that there was a marked difference in survival in teredos 

 from different piles. With conditions apparently the same for all the 

 piles, it seems reasonable to assume that the difference of survival 

 was due to differences in the porosity of the wood in the piles, which 

 would allow diffusion to take place more rapidly in some piles than in 

 others. This phenomenon is difficult to account for in any other way. 



Although the above evidence is far from conclusive, the explana- 

 tion given seems to be the only one which accounts for some of the 

 phenomena observed. Hence it seems reasonable to assume that 

 when plugged up in their burrows teredos are killed only by a gradual 

 reduction in salinity of the water in the burrow, and that this process 

 takes place by diffusion through the wood. 



