440 " THETIS " SCIENTIFIC RESULTS. 



anterior msopliagus is bent sharply forward, where it issues from 

 the proboscis, at the posterior end of the sac. *The posterior 

 oesophagus is bent back on itself, where it passes through the 

 nerve-ring, at the anterior end of the body cavity ; it then 

 receives the duct of the oesophageal gland, and passes back, along 

 the left side of the cavity, through the pericardium, and up the 

 axis of the coil to the stomach. 



The stomach is tubular, and has a lumen not very much greater 

 than that of the posterior oesophagus ; near their junction it takes 

 a somewhat spiral course on and through the digestive gland, and 

 is joined by the intestine ; this passes through the nephridium 

 to the rectuiin lying along the mantle on the right side of the 

 cavity, the anus being situated well forward almost on a level 

 with the anterior end of the ctenidium. 



The oesophageal gland is an irregularly shaped lamella, lying 

 mostly in the anterior end of the body cavity, but having a 

 ribbon-like prolongation continued back for some distance. 



There is one pair of salivary glands situated in the anterior 

 end of the body cavity, just posterior to the nerve-ring. The 

 salivary ducts are long, in conformity with the length of the 

 proboscis. 



The digestive gland is large ; there are two ducts, one opening 

 into the pr-oximal, the other into the distal end of the stomach. 



4. Nephridium. 



This organ is situated in the usual position, immediately behind 

 the pallial cavity, on the right-hand side of the visceral coil. It 

 is rather large, and approaches somewhat to a bean in shape, the 

 convex side being in the axis of the coil. 



The glandular mass is very thick, and occupies the whole of 

 the right side of the organ ; the individual lamellae are broad and 

 short. 



The cavity of the organ is spacious, and communicates with the 

 pallial chamber either through a simple reno-pallicd orifice or per 

 medium of a small, somewhat ovoid, muscular ureter. 



The nephridial gland is well differentiated, and lies in the wall 

 separating the pericardium and nephridium ; with the cavity of 

 the latter it communicates by numerous pores ; along its lower 

 edge is the sinus which is here termed the vena-cava. 



5. Vascular system. 



The pericardium may be either large or rather small ; besides 

 the heart and aorta, it contains a section of the posterior oeso- 

 phagus. 



The heart is of the usual monotocardian type. 



