1924] Lazier: Morphology of Digestivt Tract of Teredo navalis 4.">7 



MORPHOLOGY OF THE DIGESTIVE TRACT 



The Teredinidae presenl as extreme modification of lamellibranch 



struct urc. In most of tin- oriran systems, however, the modification is 

 mainly of shape and position while relations ami essential features 

 remain typical. The body is greatly elongated, the visceral mass 

 occupying approximately the anterior fourth of its Length, and the 

 grills, the remainder. The small, globular shell covers onlj the anterior 

 tip of the animal; most of the organs therefore lie behind the posterior 

 adductor muscle instead of anterior to it as in mosl bivalves. The 

 kidneys, heart, and pericardium have been elongated and rotated 

 around this muscle through an angle of 180 decrees so that their 

 morphologically posterior end becomes anterior and their dorsal side. 

 ventral. This places the renal orifices at the posterior end of the 

 viscera. Tl tier organs lie below the morphologically dorsal wall 



of the pericardium. The genital orifices have followed the renal 

 orifices posteriorly. The visceral ganglion has moved from its position 

 beneath the posterior adductor muscle to the posterior tip of the vis- 

 ceral mass. The cerebral and pedal ganglia and t heir connectives form 

 the usual ring about the oesophagus. 



The digestivt system has not been rotated but is extended poste- 

 riorly in a long loop. The mouth and anus retain their usual positions, 

 the former between the anterior adductor muscle and the foot, and 

 the latter on the dorsal side of the posterior adductor. The oesophagus 

 is the typical short, Hat, ciliated tube. The stomach, however, is 

 greatly elongated and relatively large. Its capacity is further aug- 

 mented by a long, cylindrical caecum opening from its posterior end. 

 The usual crystalline style and its mechanism are well developed, the 

 sac of the style lying in the small, discoidal foot of the animal. The 

 digestive glands are large and are closely applied to the stomach. The 

 intestine is moderately long and it does not pass through either the 

 heart or the pericardium. The anus o|"' I|s into a long, anterior diver- 

 ticulum of the suprahranchial cavity, the anal canal. .More detailed 

 comparison with typical lamellibranch structure will be made as the 

 various parts of the digestive system are considered. 



The mouth <»>.. pi. 22. fig. 1 ; pi. 23, figs. 6, 7. 8; pi. 24. fig. 9 . as 

 in most bivalves, is a small, median, transverse slit. The dorsal and 

 ventral lips are continuous, respectively, with a pair of dorsal, and 

 a pair of ventral, labial palps. The dorsal palps ■ -/. I. p.. pi. 24, 



