ORGANS OF SECRETION. lOY 



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. The 

 method of preparing sepia practiced on the shores of the Medi- 

 terranean, is to careful]}^ extract the ink-bag and dry its contents. 

 Triturated with caustic soda or potash, it is afterwards boiled 

 for half an hour with caustic lye, and finall}^ 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. So indestructible is the ink, that it is 

 frequently met with preserved with the fossil remains of Belem- 

 nites and other extinct genera. The full protection afforded the 

 soft parts by the external shell of the tetrabranchiates accounts 

 for the absence of the ink-bag in that division of the cephalopoda. 



An analj'sis of sepia shows that *78 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, t per 

 centum carbonate of magnesia, and sulphate and chloride of 

 soda 2 per centum. 



" Mr. Lloyd states, in his interesting ' 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 

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

 think, with Mr. Lloj^d, that this being the case, it is difficult to 

 perceive how, according to the generall}^ 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 

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

 be startled by the sudden appearance of masses of dark color in 

 the water, and in the confusion the cuttle makes his escape." — 

 W. R. Hughes, in Nature, ix, 363, 1874. 



Furjyle Gland (xv, 79). This gland accompanies or is a modi- 

 fication of the mucus-gland. It is only found in a portion of 

 the prosobranchiate gastropods ; among them, in both the typical 

 Muricidse and the Purpuridse ; but a similar gland secretes a 

 violet liquid in Janthina and Aplysia, and yellow in the Bullidse. 

 The peculiarity of the fluid secreted by this gland is, that origi- 

 nally colorless or yellowish, a short exposure to sunlight changes 

 it to a brilliant violet or reddish color, at the same time giving 

 off a very penetrating fetid odor.* The cause of this photo- 

 graphic change of color is unknown, but the knowledge of it 

 came to mankind in very early ages, and Tyrian purple was 



* It is colored at the moment of its secretion in Aplysia. 



