THE PAST AND PRESENT OF CUTTLE-FISHES. 759 



defense, and for enabling them to escape from their enemies. Dis- 

 charging the inky fluid through the " funnel," into which the duct of 

 the ink-sac opens, it rapidly diffuses itself through the water, and en- 

 ables the animal to escape under a literal cloak of darkness. The 

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

 the cuttle-fish have long been disputed. According to one authority, 

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

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

 to represent an intestinal gland ; while a third opinion maintained its 

 entirely special nature. The ink-sac is now known to be developed 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 specialized part of 

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

 oldest cuttle-fishes, 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 fossilized in certain extinct cuttle-fish shells. 

 Its secretion forms the original sepia color, a term derived from the 

 name of a cuttle-fish genus. The fossilized 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 fossilized ink in the preparation of the plates wherewith he 

 illustrated his "Mollusca." At the present time, recent cuttle-fish ink 

 is said to be utilized in the manufacture of ordinary artists* " sepia." 



The due regulation of cuttle-fish existence is determined by the 

 action of its nervous apparatus. The ordinary type of molluscan 

 nervous system undergoes in the cuttle-fishes a decided change of 

 form. In a snail or whelk, for example, the nervous system exhibits 

 an arrangement of three chief nerve-masses or "ganglia," connected 

 by nervous cords. Of these three nerve-centers, one is situated in the 

 head, a second in the " foot " or organ of movement, and a third in 

 the neighborhood of heart and gills, or amid the viscera generally. 

 Increased concentration of this type of nerve-arrangement awaits us 

 in cuttle-fish organization. Just as the spider possesses a more con- 

 centrated and localized nerve-axis than the insect, or as the gangliated 

 chain of the latter becomes the fused nerve-mass of the spider, so in 

 the cuttle-fish, the molluscan nerve-system, scattered and diffused in 

 the snail, whelk, or mussel, becomes localized in adaptation to the in- 

 creased nerve-control and to the wider instincts of cuttle-fish exist- 

 ence. This process of nerve-localization and concentration is accom- 

 panied by certain important modifications affecting other regions and 

 structures of cuttle-fish economy. Thus the nerve-centers are found 

 to be protected and inclosed within a gristly or cartilaginous case, that 

 foreshadows the functions of the vertebrate skull, though in no sense 

 connected with that structure. 



