A SQUID • 107 



two conspicuous white veins — the precaval veins — which pass 

 through them longitudinally from one end to the other. These 

 veins are wide, spongy- walled structures which run to the bran- 

 chial hearts and will be seen toward the median line from those 

 organs. Just beneath the base of the two kidneys and between 

 the branchial hearts is the median, or systemic, heart, into which 

 blood pours from the gills. Note a median artery, the posterior 

 aorta, which leads back from the systemic heart ; it branches into 

 three large mantle arteries, two of which pass to the right and 

 left, respectively, and enter the mantle at the side, while the other 

 passes into the mantle in the median Hne ; it is through these 

 arteries that the mantle is supplied with blood. 



On each side between the base of the gill and the rectum and 

 extending parallel with the latter organ, notice again the delicate 

 kidney ; each of the pair of kidneys extends backward to a point 

 a short distance back of the branchial heart, and forward to a 

 point back of the base of the ink bag, where it communicates with 

 the mantle cavity through a small opening. Find the two open- 

 ings by lifting up the body wall with forceps and blowing on it 

 with a blowpipe, when they will appear. 



Running back from the branchial heart on each side is a wide 

 vessel, the postcaval vein ; the forward end of this vein has thick, 

 spongy walls like those of the precavals and is easily seen ; the 

 greater part of it, however, has extremely thin walls and can be 

 seen with difficulty. Near the base of each gill note also a vessel 

 which runs forward and laterally into the mantle; this is the 

 mantle vein. Just back of this vein is a muscle which connects 

 the gill with the mantle ; it is the branchial retractor muscle. 



Note the two large stellate ganglia in the forward part of the 

 inner surface of the mantle, and the radiating nerves which each 

 ganglion sends into the mantle. 



In the hinder portion of the visceral mass in the male animal 

 observe on the animal's left (the observer's right), just behind the 

 branchial heart, a coiled tube, the vas deferens, and in the female 

 the thick-walled oviduct. Extending farther back and near the 

 median Hne is the large, white testis in the male and the large 

 ovary in the female. 



