166 ANIMAL PHYSIOLOGY. [LESSON 47. 



moreover, it affects the eyes of other animals : in the meanwhile, 

 the Cuttle-fish escapes ! 



725. The situation of this bag differs in the various species, but 

 it is usually found adjacent to the liver. 



720. The beautiful black pigment known as " Indian Ink," is 

 made by the Chinese from the inspissated (hardened) contents of the 

 ink-bag of one species, and the no less beautiful color, Sepia, from 

 the ink-bag of another species of Cuttle-fish, so that the Fine Arts 

 are greatly benefited by the means necessary to insure their lives. 



727. But the most surprising fact in this connection is, that the 

 contents of the ink-bags of a number of fossil Cuttle-fishes has been 

 made into an ink (in England), and the frontispiece of a pamphlet 

 that went through a very large edition, printed with it ; in color, it 

 bears a close relation to Sepia.* 



728. The Cuttle-fishes being shell-less, require a bone of some 

 kind for the attachment of their strong and powerful muscles, and 

 to give general support to the body. For these purposes, they are 

 provided with an internal skeleton the only animals amongst the 

 invertebrate (save certain polypes) similarly provided. This bone, 

 which extends nearly the whole length of the body, is called the 

 gladius (a sword), and is as varied in form as composition. 



729. In some species it is long, and shaped like the feather of a 

 bird, the quill portion being inordinately long, whilst in substance it 

 is scarcely cartilaginous. In the common Cuttle-fishes (Sepia 

 officinalis) , it is thick, and broad in shape, having its animal mem- 

 brane consolidated by the carbonate of lime. 



730. The bone of this animal is common in every Chemist's 

 shop, and (in this country) is placed in the cages of Canary and 

 other small birds ; considering that it is solidified by an earth so 

 weighty as carbonate of lime, it is, above all things, remarkable for 

 its extreme lightness ; we will see what causes it. 



731. Take a portion of such a bone, break it, and place it under 

 the microscope the secret of its lightness will soon be revealed. 



It will be seen that the structure consists of a number of strata, 

 or laminae, of inconceivable thinness; these are separated from each 

 other by a vast number of pigmy pillars (Fig. 267), which necessa- 

 rily admit of a current of air to pass freely between the laminated 

 plates, which not only imparts lightness to the fabric, but must give 

 great buoyancy to the animal. 



* The Author possesses a copy of the pamphlet iu question. 



