1924] Lazier: Morphology of Digestive Tract of Teredo navalis 459 



writer has seen a Teredo, which had been removed from the wood and 

 was siphoning in a dish of water, colled excess sediment in the poste- 

 rior part of the infrabranehial cavity and suddenly eject it through 

 the in-current siphon, apparently by a quick contraction of the mantle. 

 This corresponds to the action of mollusks with a closed mantle as 

 described by Kellogg (1915), except that there the adductor muscles 

 effeel the contraction. There are cilia on the sides of the foot which 

 carry particles upward to the labial palps. These ciliated tracts 

 doubtless serve to collect wood fibers rasped off in boring. The details 

 of the ciliary mechanism of Teredo remain to be worked out, but it is 

 apparent that there exists an apparatus similar to that of other 

 lamellibranchs for the capture and transportation of plankton. 



Sigerfoos (1908) does not mention the labial palps. Deshayes 

 (1845-1848) and Quatrefages (1849) both figure four long, narrow 

 ones. It is evident that these structures will prove to be of value in 

 systematic distinctions, at least for some species. 



The oesophagus (of., pi. 22, fig. 1; pi. 23, fig. 6) resembles that of 

 most lamellibranchs. It is short, dorso-ventrally compressed, and 

 heavily ciliated throughout its length. It narrows posteriorly so 

 that its width at the stomach is about one-half that at the mouth. In 

 the walls are several longitudinal furrows. 



The stomach (pi. 22, fig. 1 ; pi. 2:!, fi^s. (i, 7, 8) is long and sub- 

 cylindrical. Most of the digestive glands lie on the right side of the 

 visceral mass so that the stomach lies somewhat to the left. Its ante- 

 rior end (a. st.) is broadened toward the right and the posterior one 

 (p. st.) is somewhat dilated. 



The stomach is always found nearly empty of food. Serial sections 

 show a great deal of coagulated, lightly staining, digestive juices with 

 ;' small amount of wood fibers and plankton. This can be seen in plate 

 24. figures 10 and 11. The other parts of the alimentary canal are 

 usually full of plankton and wood chips, indicating that the passage 

 of food through the stomach is relatively rapid. 



The digestive glands, or livers, which, primitively, are paired eva- 

 ginatioiis of the walls of the stomach (Pelseneer, 1906; Sigerfoos, 

 1908), are broken up into a number of glandular masses in Teredo, 

 each emptying into the stomach by one or more orifices. The glands are 

 closely applied to the walls of the stomach so that no exposed ducts 

 are present. Food material enters the proximal lumina of at least 

 some of the duets (pi. 24. fig. 11). For convenience we have desig- 

 nated anterior, ventral, and posterior livers. None of these, excepl 

 the posterior one. is a single mass. 



