CEPHALOPODA. 451 



In the Dibranchiatc genera the liver is either undivided or pre- 

 sents only two lobes, but in other respects its composition and 

 minute structure is similar to that of the Nautilus t 



(493.) 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 intense black colour, can be poured in astonishing 

 abundance, and, becoming rapidly diffused through the surround- 

 ing 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 opaque and cloudy, that the Cephalopod remains 

 completely concealed from its pursuer, and not unfrequently en- 

 sures 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 (Jig- 21 1, 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 black- 

 ing 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. 



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

 possess a complex and elaborate circulatory system, organized upon 

 very extraordinary principles, to the consideration of which we now 

 invite the attention of the reader. 



The branchiae (Jig. 211, g, g) in all the genera now known to 

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

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

 there are four branchial organs, two on each side : and hence Pro- 

 fessor Owen has divided the class into two great orders, under the 

 names of Dibranchiata and Tetrabranckiata , the former em- 

 bracing 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. 



In both the Dibranchiate and Tetr 'abranchiate orders, each bran- 

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

 of vascular lamellae seen in the figure given below (Jig. 211, g) ; 



O r. Q 

 Xi G << 



