244 



thelium also ingest food particles. The only free enzymes in the lumen seem to be the 

 amylolytic ones set free by the dissolution of the crystalline style. Potts {loc. cit.) 

 asserts that the stomach, caecum and lumina of the livers contain no other recognizable 

 organic material except wood, and that only very occasional diatoms are found in the 

 intestine. He concludes that Teredo subsists for the most part on wood alone, being 

 almost or quite independent of plankton organisms. 



The species on which Potts worked are not stated, although he studied several 

 and came to the conclusion that his observations are applicable to the Teredinidae 

 as a group. This seems probable as regards the partial digestion of wood in the liver 

 lobules in the manner described, as the presence of wood particles in the lumina has 

 been observed h\ Sigerfoos in Bankia goiildi and by us in Teredo navalis, as well as by 

 Potts and Yonge in the species investigated b\' them. But regarding the conclusion 

 as to the non-utilization of plankton there is considerable room for doubt. 



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 present. 

 For the processes of growth and repair, considerable nitrogenous matter would be 

 required. The need for a simultaneous supply of plankton is accordingly indicated. 



While it is true, as stated by Potts, that diatoms compose a relati\ely small 

 proportion of the contents of the digestive tract, their presence is not to be regarded 

 as negligible. In specimens examined by us the stomach has contained only scat- 

 tered fragments of wood. The implication is that none of the material ingested 

 is kept for more than a brief time in the stomach, being rapidly passed on to other 

 portions of the digestive tract. In the liver lumen and in the caecum so few diatoms 

 are found that their presence may be regarded as accidental. But the intestine usually 



Fig. 92. Section through intestine of Teredo navalis, showing a number of diatoms mixed with the 

 wood particles. 



contains a number of diatom remains (see fig. 92). Careful computations ha\e shown 

 that as much as 1 1 per cent by volume of the contents of the intestine may consist 

 of diatoms and other forms which leave skeletal remains. This is too large a proportion 

 of such material to favor the assumption that it has been accidentally ingested along 

 with the particles of wood. Also, the presence of these skeletal remains in the intestine 

 would indicate the ingestion of a proportional number of flagellates and ciliates and 

 other forms which after digestion would not leave any recognizable remains. 



