536 



CEPHALOPODA. 



Fig. 222. 



mary terminate abruptly where the duct of 

 the ink-bag enters the gut (/c, fig. 221), which 

 for the small extent beyond this part is smooth 

 internally. 



In the Octopods the intestine passes through 

 the muscular septum of the branchial cham- 

 ber, immediately above which it terminates. 

 In the Decapods the rectum and duct of the 

 ink-gland are surrounded by the muscular fibres 

 which connect the pillars of the funnel to one 

 another; in both cases the fibres serve as a 

 sphincter to the anus. 



In many Dibran- 

 chiata, especially the 

 Decapods, the termi- 

 nation of the rectum 

 is provided with two 

 lateral fleshy appen- 

 dages ; for which, as 

 far as we know, no use 

 has hitherto been as- 

 signed. In the Sepio- 

 teuthis these process- 

 es (a, a, fg. 222) are 

 of a broad inequilate- 

 ral triangular form, Anal valves, Sepioteuthu. 

 attached to the sides 



of the transverse anal aperture (6) by their 

 acute angle, from which a ridge extended lon- 

 gitudinally to the middle of the base ; when 

 the processes were folded down upon the vent 

 (as in .4,^. 222), the ridge fitted into the aper- 

 ture, so as accurately to close it. In the 

 Cuttle-fish the corresponding processes are of a 

 rhomboidal form, with a thicker ridge on the side 

 next the anal aperture, which they in like man- 

 ner are adapted to defend against the entrance 

 of foreign substances by the funnel. In other 

 genera they are not adapted to defend the anus 

 mechanically, being elongated and filiform; 

 but they probably serve to give warning 

 of the presence of foreign bodies, and excite 

 the necessary contraction of the constrictors 

 of the gut ; Rathke" compares them to antennae 

 in the Loligopsis, where the anal processes are 

 very long (11, fig. 223). 



The apparatus for secreting the inky fluid, 

 formerly regarded as characteristic of the class 

 of Cephalopods, is wanting in the Nautilus, 

 which, as it has a large and strong shell to pro- 

 tect its body, stands less in need of such a 

 means of defence : the ink-bag is, however, 

 present in the Argonauta. 



The ink-bag (/, fig. 221) varies in its re- 

 lative position in different Dibranchiata: in 

 the Cuttle-fish it is situated near the bottom 

 of the pallial sac, in front of the testicle or 

 ovary. In the Calamary it is raised close to 

 the termination of the intestine; we have found 

 it similarly situated in the Argonauta, Sepioteu- 

 this, and Ilossia. In the Octopus it is buried 

 in the substance of the liver, a small part only 

 of its parietes appearing on the anterior sur- 

 face of that gland, from which its duct is con- 

 tinued forwards to terminate in this genus im- 

 mediately behind the anus. 



From this connection of the ink-bag with 

 the liver in the Poulp, Monro was led to sus- 

 pect it to be the gall-bladder. What its real 



nature may be still remains doubtful ; De Blain- 

 ville and Jacobson regard it as a rudimental 

 urinary apparatus :* Sir Everard Home f com- 

 pares it to the secreting sac which opens into 

 the rectum in Rays and Sharks, and this we 

 consider to be the true homology of the ink- 

 bag. It is interesting, indeed, to observe that 

 corresponding anal glandular cavities in the 

 Mammalia are in many instances modified to 

 serve by the odour of their secretion as a means 

 of defence, just as the part in question operates 

 in the Cephalopods by reason of the colour of 

 the ejected fluid. 



When the ink-bag is laid open and well 

 cleansed of its contents, its inner surface is 

 seen to be composed of a fine cellular or 

 spongy glandular substance : its exterior coat 

 is of a tough white fibrous texture, and its 

 outer surface commonly exhibits a peculiar 

 glistening or silvery character. 



The ink-bag probably attains its largest pro- 

 portional size in the genus Sepiola, where it 

 presents a trilobate form. It is of an oblong 

 pyriform shape in Sepia, Sepioteuthis, and 

 Loligo. It is relatively larger in Sepia than 

 in Octopus, and the quantity of water which 

 its contents will discolour is very surprising: 

 it behoves the anatomist, therefore, to be very 

 careful not to puncture this part during the 

 dissection of a Cephalopod. 



In the living Cephalopods the inky fluid is 

 secreted with amazing rapidity ; we have seen 

 an Octopus, which had previously discoloured 

 the water for a considerable extent around it, 

 immediately after its capture continuing its 

 black ejections several times in quick succes- 

 sion, and ultimately expelling in convulsive jets 

 a colourless fluid, when the powers of secreting 

 the black pigment were exhausted. 



In every species of Cephalopod which pos- 

 sesses this organ, the tint of the secretion cor- 

 responds, more or less, with the coloured spots 

 on the integument. The Italian pigment, 

 called ( Sepia/ and the Chinese one, com- 

 monly called ' Indian Ink,' both of which are 

 the inspissated contents of the organ above 

 described, afford examples of different shades 

 of this singular secretion. 



If the Cephalopods are enabled thus to con- 

 ceal themselves during the day, they have also 

 the power, by means of another secretion, to 

 render themselves conspicuous by night by 

 means of a phosphorescent exhalation.^ 



The Liver. This gland is remarkable in the 

 Cephalopods, as in the other classes of the Mol- 

 luscous Sub-kingdom, for its great proportional 

 size. In the Nautilus the liver (q, q, Jig. 219) 

 extends, on each side of the crop, from 

 the oesophagus to the gizzard. There is a 

 parallelism of form, as will be afterwards seen, 

 between this gland and the Respiratory organs, 



* Davy states that the secreted fluid is " a car- 

 bonaceous substance mixed with gelatine j" but, 

 according to Bizio, this secretion yields on analysis 

 a substance .ini generis, which he calls ' Melauia.' 

 See Edinb. Phitos. Journal, vol. xiv. p. 376. 



f Lectures on Comp. Anat. vol. i. p. 398. 



| See Oligerus Jacobaeus de Sepiaeluce, in the 

 Acta Hafniens. vol. v. p. 283. 



