THE CHAMBERED NAUTILUS. 505 
species have it in the liver, others near the siphon, and others among the ~ 
viscera, There is a communication between the ink-bag and the siphon, 
so that when the ink is ejected it is forcibly thrown out together with the 
water. Thus the very effort for escape serves the double purpose of urgin g 
the creature away from danger and discolouring the watcr in which it swims, 
The animal can eject the ink with such force that it has been known to 
dedecorate a naval officer's white duck trousers with its liquid missile, the 
aggrieved individual always asserting that it took a deliberate aim for that 
purpose, 
Generally, the animal throws out its ink on the least alarm, a circumstance 
of some importance in geology. It was discovered by Dr. Buckland that in 
many specimens of fossil cephalopods, called scientifically Geoteuthis, z¢., 
Earth Squid, the ink-bag remained in the animal untouched by its long sojourn 
within the earth, and even retained its quality of rapid mixture with water. 
A drawing was actually made by Sir F. Chantrey, with a portion of “ sepia” 
taken from a fossil species, and the substance proved to be of such excellent 
quality, that an artist to whom the sketch was shown was desirous of learning 
the name of the colourman who prepared the tint. 
The curious skeleton of the Sepia, popularly called “ Cuttle-bone,” is com- 
posed of many tiers of tiny chalk pillars, which can only be seen by the aid 
of the microscope. 
ANOTHER order of cephalopods is called by the name of Tetrabranchiata 
or Four-gilled animals, because the organs of respiration are composed 
of four branchia. These creatures possess a very strong external shell, 
which is divided into a series of gradually-increasing compartments con- 
nected together by a central tube called the siphuncle. As the animal grows, 
it continues to enlarge its home, so that its age can be inferred from the 
number of chambers comprising its shell. 
In former days these creatures were very abundant, but in our day the 
only known living representative is the CHAMBERED or PEARLY NAUTILUS, 
While the animal still lives, the short tubes that pass through the walls of 
the chambers are connected by membranous pipes, and even in a specimen 
that has been long dead, these connecting links hold their places, provided 
that the shell has not been subjected to severe shocks. In one of these 
shells now before me, which I have very cautiously opened, the whole series 
of membranous tubes can be seen in their places, black and shrivelled 
externally, but perfect tubes nevertheless. 
The colour of the shell is very beautiful. The ground is white, over which 
are drawn, as with single dashes of a painter’s brush, sundry bold streaks of 
reddish chestnut, mostly coalescing above, and reaching nearly to the centre 
of the spiral. This porcelain-like material is, however, only an outer coat 
laid on the real pearly substance of the shell, which is seen on looking into 
the hollow or into any of the chambers. The Chinese avail themselves of 
this double coating, and, with the untiring perseverance of their laborious 
nature, take the greatest trouble to spoil the finest shells by covering them 
with their grotesquely unperspective carvings of figures and landscapes, cut 
so as to relieve the deep colour of the raised figures by the white pearly 
backgrotind: Unlike the shell of the argonaut, which is almost as fragile 
as if made.of sugar, that of the Nautilus is firm and s'rong, and will bear a 
considerable amount of rough handling before betraying any signs of injury. 
THE order which now comes before our notice is composed of animals 
which ‘crawl upon a broad muscular organ, termed, from its use, the foot. 
It is an enormously large order, containing all the snails, whether terrestrial, 
aquatic, or marine, the whelks, limpets, and similar animals not so familiarly 
known. Many species are much used as food, while others are of great 
