238 



stance of even more rapid destruction is furnished l)\- piling dri\en in a pipe line to 

 a dredge near the Southern Pacific Oakland Mole on or about May 22, 1923, and 

 removed October 22. Some of these piles were entirely destrcn-cd at the mud line 

 by Bankia, as illustrated in figs. 89 and 9U. This destruction had accordingly occurred 

 in 5 months or possibly less. The piling, being alread\' watersoaked, was doubtless 

 attacked soon after the dri^•ing. 



The Wood Used as Food 

 The question whether or not Teredo derives any nourishment from the wood in 

 which it bores has been almost as much debated as the problem of the method of 

 boring. As has been pre^•iously stated, the particles of bored wood are normally 



T': 



.| ^Pl.r|MVi.PH-inHM.rjti!j-lj);.f |'i;|. 



Fig. 89. Breaking point, near mud line, of pile at Oakland Mole, destroyed within 5 months by 

 Bankia setacea. 



swallowed, and later extruded from the burrow through the anal siphon, after passage 

 through the digestive tract. The fact that the caecum is always found filled with the 

 borings is of itself no proof that they are in process of digestion. The caecum might 

 conceivably be merely a reservoir for temporary storage of the particles, in order to 

 keep them separated from the plankton food. The presence of the well developed 

 typhlosole throughout the length of the caecum, however, and the fact that this 

 typhlosole is supplied with blood from a large arter>- direct from the heart, afford 

 considerable evidence that nutritive substances are removed from the wood during 

 its temporary lodgment in the caecum. On a priori grounds, also, it would be sur- 

 prising If Teredo were entireh' to neglect so pro.ximate a source of food as is afforded 

 by the wood particles passing through its digestive tract. 



Ne^•ertheless, it has been somewhat generally assumed that the wood particles 

 are merely mechanically handled by the borers and extruded from the burrow chemi- 



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