224 DIVISION II. MOLLUSCOUS ANIMALS.— CLASS I. CEPHALOPODS. 
rapidly appear and disappear, so that the same Cephalopod is one moment 
white and the next yellow or brown. The surface of the skin also changes 
its nature under the influence of excitement. For instance, in the Octopus, 
when tranquil, it is perfectly smooth, but as soon as the animal is disturbed, 
the body, the head, and even the arms appear covered with tubercles and 
elevations, where an instant before nothing of the kind was to be seen. 
It might be supposed that the Cephalopods, by their swiftness, their arms, 
and their powerful jaws, were sufficiently provided with means of attack or 
defence ; but nature has besides favored many of them with a remarkable 
secretory organ, producing a black fluid, and opening into the air-tube. 
When the animal is in danger, or wishes to avoid observation, it ejects a 
sufficient quantity of this inky liquid to form a thick cloud in the water, 
which serves to conceal it from its foe. This black sepia-juice is, as we all 
know, used as a pigment, the durability of which may be inferred from the 
fact that even the contents of the ink-bag of fossil species have still been 
found useful. It has been affirmed that grains of wheat, buried with Egyp- 
tian mummies three thousand years ago, have germinated ; but it is surely 
still more astonishing that an animal secretion, the origin of which is lost in 
the dark abyss of countless ages, should have remained so long unaltered. 
The Cephalopods are scattered in countless numbers over the whole ocean. 
Some, like the Argonaut, constantly frequent the high seas; others, like the 
common Octopus, invariably cling to the coasts. Two pelagic species — 
Onmastrephes giganteus and sagittatus—leave annually, the first the South, 
the second the North Polar Sea, and wander in enormous shoals to the 
coasts of Chili and Newfoundland. The Sepias and Calamaries appear in 
spring along the coasts, where they tarry a shorter or longer time, according 
to the difference of species, and then withdraw again into the deep. 
Almost all Cephalopods are nocturnal or vespertine in their habits. At 
night they abound on the surface of the seas, but are not to be seen during 
the day. With the exception of the Poulp or Octopus, which leads a soli- 
tary life on rocky coasts, they love the society of their kind, and wander in 
troops along the shores and in the deeper ocean. They are all of them 
extremely voracious, destroy on shallow banks the hopes of the fisherman, 
devour on the high seas countless myriads ef young fish and naked mollusks, 
and kill, like the tiger, for the mere love of carnage. Thus they would 
become dangerous to the equilibrium of the seas, if nature, to counterbal- 
ance their destructive habits, had not provided a great number of encmies 
for the thinning of their ranks. They form the almost exclusive food of 
the sperm whales and dolphins, and various sea-birds love to skim them 
from the surface of the ocean. Tunnies and bonitos devour them in vast 
numbers, the cod consumes whole shoals of squids, and man catches many 
millions to serve him as a bait for this valuable fish. 
