A SQUID 129 



The excretory system. The kidneys and their external openings 

 have already been observed. As in other mollusks, the kidneys 

 also communicate with the pericardial space. 



The circulatory and respiratory systems. Pushing aside the 

 organs which partly conceal it, observe again the systemic heart; 

 note its shape and slightly asymmetrical position. Extending 

 from its forward end is the anterior aorta, which takes blood to 

 the forward part of the body ; its course cannot be followed at 

 present. The hinder part of the body is supplied with blood by 

 the posterior aorta. This vessel, as we have already seen, leaves 

 the hinder end of the systemic heart; it sends off two pairs 

 of small arteries to the stomach and to other viscera, and then 

 branches into the three mantle arteries already mentioned. Find 

 them all and trace them as far as possible. Observe again the 

 two branchial hearts. Note the branchial artery, by which blood 

 passes from the branchial heart to the gill; also the branchial 

 vein, through which it passes into the systemic heart. 



Observe again the veins which bring the blood to the bran- 

 chial hearts. The precavals bring blood from the forward part 

 of the body. Trace them forward. They enter the kidneys 

 near the forward end of those organs and traverse their glan- 

 dular walls back to the branchial heart. Press aside the rectum 

 and the forward end of the kidneys, and observe where the 

 two precavals come from beneath and enter the kidneys. With 

 fine scissors cut the connective tissue which binds the veins, 

 and also the mesentery which holds down the rectum and the 

 ink-bag, and turn these organs back. Trace the two precavals 

 forward; they will be seen to come from a delicate median 

 vein which may be followed into the head. Observe again 

 the postcaval veins, which bring blood from the hinder part of 

 the body and join the branchial hearts near the same place 

 as the precavals. Their forward ends also traverse the glan- 

 dular walls of the kidneys and are here conspicuous; back of 

 these they are much wider, but are very thin- walled and not 



