Introduction to Animal Morphology. 319 



middle line of the mantle cavity, usually communi- 

 cating with the funnel in an anus either round (Nauti- 

 lus), or with one, two, three, or (in Sepia) four 

 triangular anal valves ; largest in Sepioteuthis ; 

 thread-like in Loligopsis ; the flexure of the intestine 

 is neural. 



The liver is reddish yellow, witn four loose lobes 

 in Xautilus ; two separate (Sepia), or transversely 

 united (Rossia) lobes ; firm and compact in others. 

 Yellow, firm lobules (pancreatic lobes), which commu- 

 nicate with the two bile ducts, are easily distinguished 

 in most forms. 



All but Nautilus have an ink bag, a long sac with 

 a lamellar iridescent lining, and a slender duct open- 

 ing near or into the anus (Decapoda). In Octopus it 

 is imbedded in the liver ; in Sepiola it becomes 

 periodically enlarged, and divided into one central 

 and two lateral parts, which show regular contrac- 

 tions. The secretion of this bag is septa, composed of 

 melanin, magnesic and calcic carbonates, and mucus. 

 These animals hide themselves, when pursued, by 

 darkening the water with this fluid. This sac is de- 

 veloped as a diverticulum from the chamber of the 

 anal tubercle, and this is primarily a segmentation 

 from the alimentary canal. In Cephalopods the sys- 

 temic heart lies at the floor of the visceral cavity, and 

 consists of a round or transversely oval ventricle, with 

 striped muscles in its walls. It has a valve at each of 

 its auricular and arterial openings. There are two 

 auricles (four in Xautilus, Fig. 31, B). There arc two 

 aortae, arising one at each end of the heart S.-pia, Lo- 

 ligo, Fig. 3 1, C), or close together (Octopoda, Fig 31, D). 

 The cephalic aorta is the largest, and gives offpallial, 



