217 



ain>l()liuc IfrniLMits which it cdntains arc set Iruc to aitl in ciigL'slion. The style of 

 Teredo (huihtless liinrtioiis in a siniihir manner. 



From the left antero-dorsal wall of the stomach projects a small, pointed diverti- 

 culum, the dorsal caecurr.. This caecum is ciliated internally. Between the dorsal 

 caecum and the orifice of the sac of the crystalline style is a distinct outpocketing of 

 the wall, which we have referred to as the lateral poinii. It is overhung by a peculiar 

 roll of epithelium. 



In lamellibranchs there is typically a typhlosole in the intestine extending more 

 or less throughout its length, and as a rule, anteriorly into the stomach. In Teredo 

 navalis this typhlosole, which we shall call the gastro-intestinal typhlosole, originates 

 at the hepatic orifice in the lateral pouch, passes across the stomach below the opening 

 of the oesophagus and posteriorly along the right ventral wall to the posterior hepatic 

 orifice, which it enters. After circling the lumen of the posterior liver, it emerges at 

 the dorsal edge of the orifice and passes posteriorly and \entrally into the intestine. 

 Its fate there will be described in connection with the latter organ. I'^rom the hepatic 

 orifice to the intestine, a small ridge lies opposite the free edge of this typhlosole. 

 The gastro-intestinal tyi)hlosole is ciliated throughout its entire length. 



A second fold, which we may call the gastric typhlosole, originates in the dorsal 

 caecum, passes above the opening of the oesophagus and, running parallel to the 

 previously described typhlosole, extends to the posterior hepatic orifice, where it ends. 

 A low ciliated ridge parallels its free edge and continues on abo\'e the hepatic orifice 

 and down to end beneath the right one of the two folds lying in the caecal orifice. 



Between this ridge and the one accompanying the gastro-intestinal typhlosole 

 is a row of small transverse folds in the wall of the stomach. They extend from the 

 posterior end of the gastric typhlosole to the fold imder which the ciliated ridge ends. 

 From the outer (left) fold in the caecal orifice, around to the right fold, in a spiral 

 course, is another row of more pronounced wrinkles and pockets. The appearance 

 of these on the outside of the stomach is shown in figure 78. The function of these 

 two rows of irregular corrugations, which are of practically constant occurrence, is 

 probably to increase the surface or the capacity of the stomach. 



There is a small ridge, or lip, above and below the opening of the oesophagus 

 into the stomach. The ventral one extends some distance to the left between the dorsal 

 caecum and the lateral pouch. 



Cilia do not cover the whole interior of the stomach as in more generalized bi- 

 valves, but are restricted to definite regions. The ciliated ridge and the gastro- 

 intestinal typhlosole have been mentioned as being ciliated, but the ciliary mechanism 

 of the alimentary tract has not yet been fully worked out in Teredo as it has been by 

 Nelson (1918) in several other forms. A few observations on living animals, however, 

 have shown strong localized ciliary currents, and further investigation will probably 

 disclose an elaborate mechanism for handling and sorting food homologous with that 

 found in other species. The method of manipulating the wood chips which are in- 

 gested would of itself be an interesting discovery. 



The intestine, from its origin at the stomach, 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, and posterior aorta. 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. 



