LOLIGO PEALII. 95 



the anterior portion of the mantle surface and running back to the 

 branchial heart. 



e) Between the branchial hearts and a little forward is a median, some- 



what irregular, firm structure, the systemic heart. As it is con- 

 cealed by portions of the venae cavae its location need not be 

 verified until the student takes up the next dissection. 



f) The branchial veins running along the ventral surface of the gills 



return the blood from the latter organs to the systemic heart. 



g) The posterior aorta arising from the systemic heart can readily be 



seen. It is quite short, dividing almost immediately into three 

 branches. These are a median mantle artery and two lateral 

 mantle arteries. Trace the course of each of these branches, 

 h) An anterior aorta and several smaller arteries spring also from the 

 systemic heart. The course of the former will be traced in the 

 next dissection. 



Exercise 4. Complete the sketch begun in exercise 3. 



Exercise 5. Make a diagram of the circulatory system, including the gills. 

 Label the parts and indicate by arrows the direction of the blood cur- 

 rents. 



Technical Note. Use a male specimen for this dissection if obtainable. 

 Remove the entire siphon and its retractor muscles, taking care not to 

 injure any other organs. Cut away the lower surface of the head 

 until you come to portions of the alimentary canal. Carefully 

 remove also the thin body wall in the region of the visceral sac, the 

 anterior and posterior venoz cavae, the gills, and the branchial hearts. 

 The systemic heart may be freed from its attachments, but the anterior 

 aorta should not be served. 



THE DIGESTIVE SYSTEM. Note the following relations and parts, 

 making further dissections when necessary: 



a) In the head is the large bulbular pharynx enclosing near its anterior 



rim the beak. 



b) Running back from the pharynx is the slender ossophagus. Trace 



the latter to the base of the head, where it passes under a large 

 elongated glandular organ. 



