1924] Lazier: Morphology of Digestive Tract of Teredo navalis 465 



The intestine («'.), from its origin at the stomach (p., pi. 22, figs. 

 1, 3; pi. 23, figs. 6, 7; pi. 24, fig. 11), runs anteriorly a short distance 

 and bends sharply upon itself. Its course is then back, remaining 

 ventral, to the posterior end of the caecum, up around the latter and 

 forward through the gonad, passing to the left of the caecal artery 

 (c. a.) and posterior aorta (p. ao.). It goes under the posterior 

 adductor muscle, bending a little to the left and then back to the 

 mid-line, and ends on the dorsal side of this muscle in the anal canal. 

 The intestine is not as straight as it is shown in the stereogram, but 

 it makes no extensive convolutions or bends other than those indicated. 



The gastro-intestinal typhlosole enlarges in the intestine, a short 

 distance from the stomach, and coils to the right, forming the large 

 coiled typhlosole of the intestine (c. t. %., pi. 22, figs. 1, 2; pi. 23, figs. 

 7, 8; pi. 24, fig. 10). It then again resumes its former size and con- 

 tinues to the sharp bend in the intestine. From here to the anus the 

 typhlosole is entirely absent. Plate 23, figure 8, shows the dilation 

 of the intestine to two or three times its diameter elsewhere for the 

 accommodation of this unique structure. In this same figure can be 

 seen the line where the intestinal wall folds in to form the typhlosole. 

 At the distal end of the rectum are a few strands of sphincter muscle. 

 The intestine is ciliated throughout. 



Sigerfoos (1908) gives a similar description, but in his species a 

 small typhlosole extends throughout the whole intestine. Deshayes 

 (1845-1848) and Quatrefages (1849) describe the intestine as being 

 of uniform diameter throughout, indicating the absence of a coiled 

 typhlosole. At the same time the intestine is longer and much con- 

 voluted, though its general course through the body is similar. These 

 two distinct types of intestine are easily observed and should prove 

 of systematic value. The consideration of such internal characters 

 may shed some light on the badly tangled taxonomy of the group. 



The intestine is always found to be full of wood chips and the 

 remains of diatoms and other plankton. In a piece of intestine 

 removed from a small living Teredo, the contents were observed to 

 move posteriorly about one millimeter in two minutes as the result 

 of ciliary action. 



The circulation of blood in the various parts of the digestive tract 

 is still to be worked out in detail, but one of two major points may 

 be mentioned. The whole tract, including the livers, is evidently 

 bathed in blood carried in sinuses with connective tissue walls (Pel- 

 seneer, 1906). The typhlosoles, however, have a definite arterial 



