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 fsecal 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, 



