578 CEPHALOPODA. 



liver unite by repeated anastomoses, and thus form two main trunks, 

 which ultimately join, and pour the biliary secretion into the laminated 

 or pancreatic cavity (y) . 



(1547.) In the Cephalopods, as in all the Mollusca, the bile is sepa- 

 rated from arterial blood supplied by large vessels derived immediately 

 from the aorta, no system of veins analogous to the vena portce of higher 

 animals being as yet developed. 



(1548.) In the Dibranchiate genera the liver is either undivided, or 

 presents only two lobes ; but in other respects its composition and 

 minute structure is similar to that of the Nautilus. 



(1549.) In all the CEPHALOPODA, with the exception of the Nautilus 

 Pompilius, there is an orifice in the immediate vicinity of the anus, 

 through which a coloured secretion, generally of a deep-brown or in- 

 tense-black colour, can be poured in astonishing abundance ; and this 

 becoming rapidly diffused through the surrounding water, a means of 

 defence is thus provided; for no sooner does danger threaten, or a 

 foe appear in the vicinity of the Cuttle-fish, than this ink is copiously 

 ejected, and the element around rendered so opake and cloudy, that the 

 Cephalopod remains completely concealed from its pursuer, and not un- 

 frequently ensures its escape by this simple artifice. The organ wherein 

 the inky secretion is elaborated is a capacious pouch, variously situated 

 in different genera. In Octopus it is enclosed in the mass of the liver ; 

 in Loligo it is located in the immediate vicinity of the anus ; and in 

 Sepia (fig. 290, q) the ink-bag is lodged near the bottom of the visceral 

 sac. On opening it, and carefully washing away by copious ablution the 

 ink within, the cavity of the ink-bag is seen to be filled up with a 

 spongy cellulosity, wherein the blacking material had been entangled ; 

 and from this cellular chamber a duct leads to the outward orifice, 

 through which the dark secretion is ejected at the will of the animal, and 

 squirted from the extremity of the funnel. 



(1550.) The CEPHALOPODA breathe by means of branchiae, and possess 

 a complex and elaborate circulatory system, organized upon very extra- 

 ordinary principles, to the consideration of which we now invite the 

 attention of the reader. 



(1551.) The branchiaa (fig. 290, gg)'m all the genera now known to 

 exist, with the exception of the Nautilus, are two in number, on6 

 situated on each side of the body ; but in the Nautilus Pompilius there 

 are four branchial organs, two on each side ; and hence Professor Owen 

 has divided the class into two great orders, under the names of Dibran- 

 chiata and Tetrabranchiata, the former embracing all the ordinary 

 genera, while the latter is, as far as we know, only represented in 

 modern times by the Pearly Nautilus, depicted in a preceding figure. 



(1552.) In both the Dibranchiate and Tetr abranchiate orders, each 

 branchia consists of a broad central stem, to which is appended a series 

 of vascular lamellae, seen in the figure given below (fig. 290, g) : by this 



