128 INVERTEBRATE ZOOLOGY 
while the other passes into the mantle in the median line; 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 openings by lifting up the body-wall with forceps 
and blowing on it with a blow-pipe, 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 line is the large white testis in the male and 
the large ovary in the female. 
Exercise 2. Make a large sketch of the mantle cavity of the 
animal showing these organs, and label all. 
With fine scissors and forceps carefully dissect away the deli- 
cate transparent body-wall and expose the organs beneath, 
taking care not to injure them. 
