211 



the lull. Its antc'rior (.•lul is l)r()a(leiK'd tow.irtl the ri.nlit, diul the posterior end is 

 somewhat cUhited. 



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

 deal of coagulated, lightly staining digestive juices, with .i small amount of wood 

 fibers and plankton. This can be seen in figure 79. The other parts of the alimentary 

 canal are usually full of \vt)od chi]")s or mingled wood chips and plankton, indicating 

 that the passage of food through the stomach is relatively rapid. 



The (li;^estivc olavds or livers, which primitively are paired evaginations of the 

 walls of the stomach, are broken up into a number of glandular masses in Teredo, 

 each emptying into tlu' stomach by one or more orifices. The glands are closely applietl 

 to the walls of the stomach, so that no exposed ducts are present. Food material 

 enters the limiina of at least some of the ducts. For convenience we have designated 

 anterior, \entral, and posterior lixers. None of these except the posterior one is a 

 single mass. 



In the pedal region there is a considerable amount of digestive gland, the anterior 

 liver [a.l., figs. 77 and 78). This communicates with the stomach by several orifices of 

 varying sizes in the right wall, and by one in the left wall. The latter orifice is in the 

 anterior wall of the lateral pouch (/./>., fig. 78). 



The \entral li\ers (v.l., figs. 77 and 78) are small, and communicate with the 

 stomach by four small orifices {v.l.o., fig. 77). 



The posterior liver (p.l., figs. 77, etc.) is a large gland lying on the right side of 

 the stomach at its posterior end. Its large duct opens to the stomach by a \-ery large 

 circular orifice. Deshayes (1848) describes many hepatic orifices in this region, instead 

 of the single large one found here and in Sigerfoos' (1908) species. 



Although the posterior li\er is externally a unit, it is di\ided into two [larts 

 differing histologicalK'. The cells composing the dorsal part are columnar, making the 

 walls of the acini thick, while the cells of the ventral part are hardly higher than the 

 diameter of their nuclei. This differentiation is indicated diagrammatically in fig. 77, 

 and the external appearance is shown in fig. 78, 3. The difference in the appearance of 

 the tissues is quite marked in the photomicrographs, fig. 79, 1-3. Sigerfoos (1908) and 

 Potts (1923) describe this same condition. The anterior and ventral livers present 

 no such differentiation. 



Besides the livers, the stomach bears four other di\erticula : the caecum, the sac 

 of the crystalline style, the dorsal caecum, and the lateral pouch. The most con- 

 spicuous is the large posterior caecum. This equals or exceeds the stomach in capacity. 

 It is cylindrical in shape, but the ventral wall is infolded to form an elaborate, two- 

 coiled typhlosole (c.t.) extending its entire length. This caecum is always found full 

 of wood chips, and it is here presumably that digestion and absorption of wood prin- 

 cipally takes place (see, however, p. 243). Only rarely have evidences of plankton 

 been tound in it, although they are common in the intestine. The great capacity of 

 the caecum allows the wood, which is probably slow to digest, to remain there for 

 some time. The typhlosole has a large area for absorption, and has an adequate 

 blood supply. A large artery carries aerated blood directly from the heart to the 

 anterior end of the caecal typhlosole. The term caecal artery seems appropriate for 

 this vessel (c.a., figs. 77 and 79). After passing through the typhlosole the blood 

 bearing assimilated food flows into the sinuses in that part of the body. 



Sigertoos (1908) states that the interior of the caecinn in the species he studied is 

 ciliated. X'one of the present writers' preparations show any cilia whatever in the 

 caecum, nor are the cells of the tall colunmar variety which usually bear cilia. The 

 caecum of a li\ing animal, just remo^■e<l from the wood, was opened and the contents 



(Continued on page 215) 



