304 



TEREDO ITS FOOD. 



their intestine to be vegetable sawdust ; but I agree with 

 Fig. 55. * Sir E. Home in thinking (as Sellius, indeed, 

 long before asserted), that the sawdust serves 

 only as a substance in which the real food 

 procured from the sea is entangled and pre- 

 vented from escaping too readily from the sto- 

 mach. f I will give you Sir Everard's descrip- 

 tion of the digestive organs of these animals, 

 which a comparison will prove to be altogether 

 different from those of the more typical bi- 

 valved mollusca. J The oesophagus (Fig. 55, a) 

 is now very short, and lies on the left side of 

 the neck : the canal swells out, and becomes 

 stomach (5), which, in its external appearance, 

 is a large bag, extending the whole length of 

 the cavity of the abdomen, but when laid open 

 it is found to have a septum (c) dividing it 

 longitudinally into two equal portions, except 

 at the lowest part, where they communicate (d), 

 the septum being wanting. The intestine has 

 its origin close to the termination of the oeso- 

 phagus, is extremely small, dilates into a cavity 

 containing a hard white spherical body the size 

 of a pin's head, and then makes a turn upon 

 itself. The course it follows is shown by the 

 letters e in the cut. J 



* This figure represents the course of the stomach and 

 intestines of Teredo navalis, removed from the hody. a, 

 The resophagus ; b, the stomach ; c, the septum, dividing 

 it into two cavities ; d, the aperture hy which the two cavi- 

 ties of the stomach communicate ; e, the course of the in- 

 testine to its termination. Comp. Anat. t. 80. 



+ See Hancock in Ann. and Mag. N. Hist. ser. 2. ii. 232. 



i Home's Comp. Anat. i. 373. 



