162 MOLLUSC A 



1. The posterior aorta divides almost immediately into 

 three large vessels. These are: 



(a) The median mantle artery which follows the edge of 

 the ventral mesentery to the mantle. 



(b) A pair of lateral mantle arteries which diverge poste- 

 riorly and supply the two sides of the mantle. Besides these 

 large vessels there is a small vessel that runs anteriorly over 

 the ventral surface of the heart and supplies the ink gland 

 and rectum, and another one that runs dorsally and poste- 

 riorly to supply part of the reproductive system. 



2. From the dorsal surface of the heart, near its anterior 

 end, a small vessel passes over the anterior and dorsal sur- 

 faces of the stomach and finally passes into the gonad. 



3. The anterior aorta is larger than the posterior aorta. 

 From the anterior angle of the heart, which is to the right of 

 the median line, it follows a straight course alongside the 

 esophagus to the head. A number of small vessels are given 

 off along its course, and it is finally distributed to the head 

 and arms. 



Draw the vessels connected with the systemic heart, into 

 the figure you have just made. 



Nervous System. — The stellate ganglia may be seen 

 through the transparent lining of the mantle, on either side 

 of the neck, where the body joins the mantle. They send 

 nerves to the mantle and are joined to ganglia in the head 

 (the infra-esophageal) by connectives. Why does the mantle 

 need such large special ganglia? Other small ganglia are 

 situated in the body, but the large and important ones are 

 grouped in the head, where they are supported and protected 

 by cartilages. 



With a razor make a median sagittal section of the head 

 of a squid and notice: 



1. Dorsal to the esophagus a rounded mass, the supra- 

 esophageal ganglion, which is supposed to represent the fused 

 cerebral ganglia. 



2. Ventral to the esophagus the elongated infra-esophageal 



