THE MANTLE-COVERED ANIMALS. 129 
stomach of the octopus by his fleshy tongue armed 
with horny hooks. But what gives the arms of the 
octopus such power ? If you look at the under 
surface of them you will find, arranged in pairs along 
each arm, suckers (s, Fig. 49), large near the mouth 
and growing small as the strips taper to a point, and 
crowded so thickly that an ordinary-sized octopus 
with arms about a foot and a half long will have 
nearly 2000 of them. Each of these suckers is a 
perfect little air-pump with a piston in the middle, 
and the moment the octopus lays an arm upon any 
creature, a muscle draws the piston in each sucker 
back. This causes it to cling like a cupping-glass, 
and the more the victim struggles the tighter is the 
grasp ; while the octopus holding by the suckers of 
his other arms to the rock has a firmer and firmer 
hold the stronger the resistance. 
One would almost imagine at first sight that long 
experience would have taught the fishes and crabs to 
keep out of the way of such a monster ; but the 
octopus has another, and almost unfair, advantage. 
He carries in his transparent skin cells of colour, 
yellow, blue, red, and brown, and has the power, like 
the chameleon, of changing colour and assuming the 
tint of the rock under which he hides. 
"New forms they take, and wear a borrowed dress, 
Mock the true stone, and colours well express. 
As the rock looks they take a different stain 
Dappled with gray, or blanch the livid vein." 
By this means he not only lies safely in wait to 
pounce upon his prey, but may himself escape the 
notice of the dolphins or the conger eels, which are 
K 
