PURPLE SECRETIONS. 241 



Sepia ; Cuvier found it more like that of the Octopus and 

 Loligo ; but different kinds of that substance are brought 

 from China, probably made from different genera of these 

 animals, where they abound of gigantic size. * At the 

 present day, according to Cuvier, an ink is prepared from 

 the liquor of these animals in Italy, which differs from the 

 genuine China ink only in being a little less black, f Davy 

 found it to be "a carbonaceous substance mixed with gela- 

 tine ; " but, on a more careful analysis, Signor Bizio pro- 

 cured from it a substance sui generis, which he calls melania. 

 " The melania is a tasteless, black powder, insoluble in al- 

 cohol, ether, and water, while cold, but soluble in hot water : 

 the solution is black. Caustic alkalies form with it a solu- 

 tion even in the cold, from which the mineral acids preci- 

 pitate it unchanged. It contains much azote : it dissolves 

 in, and decomposes, sulphuric acid : it easily kindles at the 

 flame of a candle : it has been found to succeed, as a pig- 

 ment, in some respects better than China ink." % 



5. Purples. — Several of the Gasteropods secrete a liquor 

 analogous, in some respects, to the ink of the cuttle-fish. 

 The Aplysiae pour out at will, or when molested, an abund- 

 ance of a beautiful purple fluid ; so that a single individual 

 can colour the water for some yards around it. This fluid 

 is secreted in a gland of a triangular figure, situated under 

 the base of the fleshy coverlid of the branchiae, and oozes 

 out from all the free surface of this coverlid. § Cuvier says, 



* Edinb. Phil. Journ. xvi. 316. t Mem. i. 4. 



j Edinb. Phil. Journ. xiv. 376. In 1815, Dr. Prout gave the following 



analysis of the colouring matter, or ink, ejected by the cuttle-fish : one 

 hundred parts contain : 



" Peculiar black colouring matter 78-00 



Carbonate of lime 10*40 



Carbonate of magnesia 7-00 



Muriate of soda 1 I 2-16 

 Sulphate of soda ? S 



Animal matter analogous to mucous - 84 



Loss 1-60 



100 00" 

 " This substance, from the length of time which it takes to subside in 

 water, appears admirably contrived for the purpose of concealing the animal 

 from its enemies, &c. A property also which, added to the permanent 

 nature of its colour, must, as Mr. Kemp observes, render it valuable as an 

 ink, or web-colour." — Ann. Philosophy, v. 419, 420. 



§ Professor Goodsir says, " Aplysia punctata secretes from the edge and 

 internal surface of its mantle, a quantity of purple fluid. The secreting 

 surface of the mantle consists of an arrangement of special nucleated cells. 

 Those cells are distended with a dark purple matter." He says the same 

 of the Ianthina.— Anat. and Pathol. Obs. 23, 24. 



R 



