ORDER I. THE OCTOPODS. —THE DECAPODS. 223 
being able to move upon their stalk in every direction. The Decapod can 
also voluntarily draw in or stretch out its claws like the cat, and thus runs 
no risk of entangling itself when shooting backwards through the water. 
The size of the arms and the arrangement of the cups differ very much in 
the various species. Thus, in the common Octopus, the arms are almost of 
equal length ; in the Philonexis there are four long and four short ones; and 
in the Argonaut two of them expand sail-like at their extremity. In the 
decapodal Calamaries and Sepias, the two feeler-like arms are considerably 
lengthened, and in the Loligopsis, the disproportion is so great that these 
organs are several times longer than the whole body. In the Octopods, 
which generally lead a more sedentary, creeping life, and clinging to stones, 
seize the passing prey, the arms, in accordance with their wants, are always 
longer, more fleshy, and stronger than in the actively swimming Decapods, 
In some species we find the arms separated; in others, they are united 
by a membrane. The Octopus has on each arm a double row of cups or 
suckers, the Sepia four rows, the Eledone but one. So wonderful are the 
variations which nature, that consummate artist, plays upon a single theme! 
so inexhaustible are the modifications she introduces into the formation of 
numerous species, all constructed upon the same fundamental plan, and all 
equally perfect in their kind ! 
When a Cephalopod has got hold of a fish or crab, the arms, by sucking 
or hooking, instantly convey the helpless prey to the mouth, where it is 
pitilessly crushed by two powerful horny or calcareous jaws, fitting one 
over the other like the mandibles of a tortoise. 
Besides their arms, by help of which the Cephalopods either swim or 
ereep, the forcible expulsion of the water through the air-tube serves them 
as a means of locomotion in a backward direction. By those which have 
an elongated body, and comparatively strong muscles, this movement is 
performed with such violence that they shoot like arrows through the water, 
or even, like the flying-fish, perform along curve through the air. Thus 
Sir James Ross tells us, that once a number of cuttle-fish not only fell 
upon the deck of his ship, which rose fifteen or sixteen feet above the water, 
and where more than fifty were gathered, but even bolted right over the 
entire breadth of the vessel, like a sportsman over a five-barred gate ! 
Finally, the fin-like expansion of their mantle renders the nimble Deea- 
pods good service in swimming. In the Sepias, this finny membrane runs 
along the sides of the body ; in the Calamaries it is situated at its extremity. 
The skin of the Cephalopods offers some remarkable peculiarities. It is 
coyered with variously-colored spots, which, as long as the animal is quiet, 
are nearly invisible, but as soon as it is excited, increase to about sixty 
times their former size ; and then, by alternate contractions and expansions, 
