1923] Dun-Miller: The Digestion of Wood by Teredo navalis 385 



indefinite period with no contact with the wood whatever. Finally, 

 wood that has passed through the digestive tract of the animal is 

 shown by microscopic study to have retained its cellular structure 

 (pi. 18, fig. 1), and some investigators even claim to have identified 

 the kind of wood by its odor and color, as stated by Moll (1914, p. 

 526). This writer remarks that it is hardly conceivable that action 

 on the wood by the digestive fluids should not have changed it more. 



In reply to these arguments it may be said that Teredo is one of 

 the most highly specialized of the boring mollusks, and might be 

 expected a priori to differ from its rock-boring relatives in its method 

 of obtaining nourishment. Some other types of animal are known 

 to derive nutriment from wood, notably the termites (Banks and 

 Snyder, 1920, p. 94) and various wood-boring beetles; among the 

 mollusks, certain snails are known to secrete enzymes which act upon 

 cellulose (Billard, 1914, p. 566). It would be surprising if Teredo 

 were entirely to neglect so proximate a source of food as is afforded 

 by the wood particles passing through its digestive tract. While the 

 animal does sometimes partition itself off anteriorly from contact with 

 the wood, it does not ordinarily do this until well grown, and probably 

 not until forced to cease boring by the honeycombed condition of the 

 wood. As regards the wood's retention of its physical properties 

 after passage through the digestive tract, we may refer to Konig's 

 observation (1913, p. 1101) that when cellulose is dissolved from wood 

 by means of strong acids, the residual lignin still possesses the original 

 woody structure. Hence we should expect that the appearance of the 

 wood under the microscope would not be materially changed, even 

 though the cellulose, hemicelluloses, and soluble sugars were entirely 

 removed. 



The most potent presumptive evidence in favor of the digestion 

 of wood by Teredo is found in the anatomical structure of the diges- 

 tive tract. The stomach opens posteriorly into an expanded and 

 elongated blind sac, the caecum, in which the wood particles swallowed 

 during boring operations are accumulated, being then periodically 

 emptied into the intestine, whence they pass into the anal canal and 

 are ejected through the dorsal siphon. It seems improbable that so 

 specialized an organ as the caecum should have no significance in the 

 economy of the animal except as a temporary storage place for 

 extraneous sawdust on its way to the outside. The anatomical 

 evidence on this point will be treated by Lazier in a paper shortly to 

 appear in this series. 



