96 STUDIES IN LIFE AND SENSE. 



wise described in certain members of the cuttlefish class a series of 

 minute pores, by which water enters the great veins and mixes with 

 the blood. It is also certain that water enters the general body 

 cavity and bathes the organs of the animal, thus converting that 

 cavity into a physiologically active space, possessing an influence on 

 the circulation in that its contained water presents a medium for the 

 conveyance of oxygen into, and for the reception of waste materials 

 from, the blood. 



Connected on the one hand with the digestive system, and on 

 the other with the more purely glandular structures of the body, is 

 the organ known familiarly as the " ink-bag " of these animals. The 

 cuttlefishes are well known to utilise the secretion of this sac as a 

 means of defence, and for enabling them to escape from their 

 enemies. Discharging the inky fluid through the "funnel," into 

 which the duct of the ink-sac opens, it rapidly diffuses itself through 

 the water, and enables the animal to escape under a literal cloak of 

 darkness. The force of the simile under which an over-productive 

 writer is likened to a cuttlefish, may be understood and appreciated 

 when the physiology of the ink-sac is investigated. It is this feature 

 of cuttlefish organisation which Oppian describes when he informs 

 us that 



Th' endangered cuttle thus evades his fears, 



And native hoards of fluid safely wears ; 



A pitchy ink peculiar glands supply, 



Whose shades the sharpest beam of light defy ; 



Pursued, he bids the sable fountains flow, 



And wrapt in clouds, eludes th' impending foe. 



The exact nature and relationship of this ink-sac to the other organs 

 of the cuttlefish have long been disputed. According to one authority, 

 the ink-bag represented the gall-bladder, because in the octopus it is 

 embedded in the liver. From another point of view, it was declared 

 to represent an intestinal gland ; whilst a third opinion maintained 

 its entirely special nature. The ink -sac is now known to be deve- 

 loped as an offshoot from the digestive tube : and, taking development 

 as the one infallible criterion and test of the nature of living structures, 

 we may conclude that it represents at once a highly specialised part 

 of the digestive tract, and an organ which, unrepresented entirely in 

 the oldest cuttlefishes, has been developed in obedience to the 

 demands and exigencies of the later growths of the race. It is this 

 ink-sac which is frequently found fossilised in certain extinct cuttle- 

 fish shells. Its secretion forms the original sepia colour, a term 

 derived from the name of a cuttlefish genus. The fossilised sepia 

 has been used with good effect when ground down. The late Dean 

 Buckland gave some of this fossil ink to Sir Francis Chantrey, who 

 made with it a drawing of the specimen from which it had been taken ; 

 and Cuvier is said to have used this fossilised ink in the preparation 



