A SQUID 127 
Notice in the mantle cavity the pair of plumose gills to 
the right and the left of the visceral mass, each attached to the 
inner surface of the mantle by a mesentery. Between the 
retractor muscles of the siphon and extending from the base 
of the gills forward to the siphon is the rectum, which terminates 
in the anus, with its two projecting valves. Find the valves. 
Beneath the rectum is the ink-bag, and both are attached to the 
organs beneath them by a mesentery. The ink-bag communi- 
cates with the rectum by means of a duct which joins it near 
the anus; this duct may be found by slitting the rectum for a 
short distance back of the anus, when the small opening may 
be made to appear by squeezing the ink-bag and forcing the 
ink into the rectum. Together with the fecal matter from 
the intestine and other waste products, the ink is voided into 
the sea water through the siphon; its function is to cloud the 
water and thus hide the animal from its enemies. In the male 
animal notice the long, tubular penis to the right of the rectum 
(the animal’s left); if the animal is a female, the thick-walled 
oviduct will be seen in a corresponding position. 
At the base of each gill note a round disc-like body; this is 
a branchial heart, from which blood is sent into the gills; near 
each branchial heart, toward the median line and running for- 
ward alongside the rectum is an elongate, transparent structure, 
the kidney. The position of the kidneys may be determined by 
the 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 branchial 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, 
