A Cepkalopodous Mollusk. 73 



The pre-cavae unite just in front of the nephridial organs 

 and form the common vena cava. This vessel lies an- 

 teriorly in the median line, just dorsal to the ink-sac and 

 midway between the siphonal retractors. It returns the 

 blood from the ink-sac, liver, oesophagus, and head. 



The systemic heart lies in the median line between the 

 posterior ends of the nephridial organs and receives blood 

 from the right and left efferent branchial vessels, which 

 course along the free edge of the gill. 



The systemic heart gives off an anterior and a. posterior 

 aorta. The former passes directly to the head, dividing at 

 the neck into a right and a left branch. On its course it 

 gives off certain branches to the digestive organs. The 

 posterior aorta soon divides into the median and lateral 

 mantle arteries already noted. 



The cavse rest dorsally on a delicate flask-shaped bilateral 

 organ of considerable size, the "spleen." 



Make drawings illustrating the course of the blood-vessels. 



The Digestive System. - - Note the large chitinous/Vza/.r, 

 situated at the base of the circle of arms. Which jaw is 

 larger? Open the mouth and note the lingual ribbon or 

 odontophore. What is its position? Pass a probe down the 

 narrow oesophagus, and cutting along the mid-ventral line of 

 the head and neck, follow the oesophagus to its entrance into 

 the stomach. On its way it is accompanied for a short dis- 

 tance, along its ventral side, by the duct from the median 

 salivary gland, a small body which may be found enfolded 

 in the anterior end of the liver. The lateral salivary 

 glands lie on the posterior surface of the buccal-mass. The 

 liver is a large gland that extends posteriorly from near the 

 spherical buccal-mass to a point dorsal to the nephridial 



