ORGANS OF RESPIRATION, ETC. 37 



of a fine red color, and rhombohedral or rhomboido-lamellar in 

 form, giving the reactions of uric acid. 



The ink-bag (not present in Nautilus) is a tough and fibrous 

 sack, the outer coat of which is thin and silvery ; the contents 

 are discharged by a duct direct (or, as in most decapods, through 

 the anus) into the mantle opening, and thence diffused in the 

 surrounding water ; covering the movements of the animal by the 

 obscurity in which it becomes almost instantly enveloped. There 

 can be no doubt of the use of this- organ in facilitating escape 

 from danger. The ink itself was formerly used by the Chinese 

 in the preparation of Sepia or India Ink, but this substance is 

 now made from lampblack. In Italy and in Turkey the Sepia is 

 still prepared from the dried pigment of the cuttle-fish, which 

 is browned by the action of an alkali.* So indestructible is the 

 ink, that it is frequently met with preserved with the fossil 

 remains of Belemnites and other extinct genera. The full protec- 

 tion afforded the soft parts by the external shell of the tetra- 

 branchiates accounts for the absence of the ink-bag in that 

 division of the cephalopoda. 



An analysis of Sepia shows that 7S per centum is composed of 

 the black coloring matter (the Melania of Bizio), and that of the 

 residuum there is 10 per centum carbonate of lime. 7 per centum 

 carbonate of magnesia, and sulphate 1 and chloride of soda 2 per 

 centum. 



Mr. Lloyd states, in his interesting u Handbook to the Marine 

 Aquarium," "that the ink (which is viscid) does not generally 

 become diffused through the water as writing-ink would be, but 

 is suspended in the water in a kind of compact cloud till it grad- 

 ually settles down, and is dispersed in flakes." Now I quite 

 think, with Mr. Lloyd, that this being the case, it is difficult to 

 perceive how. according to the generally received opinion, the 

 retreat of the animal is covered by the ejected cloud. It seems 

 to me more likely that this discharge is to divert the attention of 

 i pursuer a dog-fish for instance which would for the moment 



* The method of preparing Sepia practised on the shores of the Medi- 

 terranean, is to carefully extract the ink-bag- and dry its contents Trit- 

 urated with caustic soda or potash, it is afterwards boiled for half an 

 hour with caustic lye, and finally the liquid is treated with an acid until 

 neutralized. After standing, a precipitate falls, which is collected and 

 dried by a mild heat, and forms the Sepia of commerce. 



