396 University of California Publications in Zoology [Vol. 22 



proportion to the amount of work to be done, it appears to be a most 

 natural arrangement, admirably adapted to its needs. The carbo- 

 hydrates of the wood therefore play an important part in supplying 

 the teredo with energy when it is most needed. 



It does not appear probable that Teredo could subsist over any 

 long period upon the wood alone, because of the negligibly small 

 amount of protein material. Especially during boring would con- 

 siderable nitrogenous matter be required. The need for a simul- 

 taneous supply of plankton is accordingly indicated. 



If the conclusion is accepted that wood tissue is partly digested 

 and absorbed as food by Teredo, some light is thrown upon the 

 probable mechanism by which toxic substances injected into the 

 timbers of marine structures protect against teredo attack. If partial 

 digestion of wood occurs, it is clear that all substances contained in 

 the wood must experience an intimate contact with the teredo '3 

 digestive fluids over a considerable period of time. Optimum con- 

 ditions then prevail for the absorption of toxic substances and their 

 effectiveness is limited only by such factors as lack of solubility, 

 inability of their solutions to penetrate the walls of the digestive 

 tract, etc., these factors being dependent upon the properties of the 

 agent and not upon the condition of exposure. Xo case of failure of 

 a given toxin to protect can be ascribed to physical isolation of the 

 borings as we might expect if the wood were regarded as wholly 

 undigested and merely mechanically handled by the teredo. 



These considerations offer practical suggestions in regard to (1) 

 the commercial preservative treatment of marine timbers, and (2) the 

 testing of the toxicity of preservative substances. We may conclude 

 that the established practice of preserving marine timbers by impreg- 

 nating the wood with toxic substances is a rational and efficient 

 process for introducing these substances into the animal's system, for 

 it is clear that the teredo cannot bore into the wood without being 

 exposed to the action of any toxins that are capable of entering 

 through its digestive tract. As to methods of carrying out toxicity 

 tests, it would appear that those methods which use the wood as a 

 vehicle for carrying the toxin possess a distinct advantage over 

 methods in which the toxin is introduced into the animal by some 

 other means, on account of the greater certainty that contact with 

 the digestive juices will occur. 



In conclusion, the authors wish to acknowledge, and express their 

 thanks for, helpful suggestions which they have received from 



