CUTTLEFISH, of which the Octopus is a familiar example, are so different from other molluscs that it is difficult to believe that they are closely related to them. They are by far the most highly organised of the group. The body is usually distinctly divided into a head and a trunk, and the head is surrounded with a crown of arms and tentacles, each of which is beset with numerous suckers for laying hold of prey. The
shell is internal (the familiar cuttle-bone of the octopus is a good example), and the foot has become modified and much altered in shape to form the arms and tentacles. The eyes are large and have much the same appearance and structure as the eye of a vertebrate, and there is a concentration of the nervous ganglia which is the nearest approach to a brain found in the Mollusca.
Just behind the head is seen the opening of a pouch, formed by the mantle being wrapped around the body, and from this protrudes the end of a siphon, known as the funnel. The funnel is the organ of locomotion, a stream of water being constantly driven out from it in a regularly pulsating manner. When the animal is stationary, the discharge from the funnel is of a mild character and directed first this way and then that in order not to disturb the surrounding water too much and to keep the body in the same position, but the moment the cuttlefish is alarmed, or wishes to pursue its prey, water is driven out in strong jets and these have the effect of driving the animal backwards through the water at a rapid rate.
INK THAT LASTS FOR THOUSANDS OF YEARS CONNECTED with the funnel is a structure peculiar to cuttle-fish, the ink-sac. This is divided into two portions, the first holding the main supply and the outer portion containing a diluted store ready for use, so that at the moment of alarm, the valve leading into the funnel is opened and each jet of water comes out as a cloud of dense black ink, under cover of which the cuttlefish retreats from its foes. Ink-sacs are commonly found as fossil remains and even now, after the lapse of countless thousands of years, it is often possible to make a usable ink from them.
Small octopus and squid are commonly met with off the coasts of the British Isles. Sometimes they may be found in rock-pools, left behind by the receding tide, although sharp eyes are needed to see them, since they possess the power, more familiarly associated with the chameleon, of changing their colour according to the background they are on. But such examples are usually very small, perhaps an inch or two across. Further out, in the deeper waters, larger examples are found, while, at rare intervals, squid, measuring five, six, or even twelve feet long are cast up during storms, particularly on the east coast.
A FEARSOME SPECTACLE: FIFTY FEET OF WRIGGLING TENTACLES STORIES of giant squid and octopus abound, but it not infrequently happens that the dimensions of the beasts are exaggerated beyond all reason. At the same time we cannot be certain how plentiful these animals are nor what is the largest size they may attain. In some parts of the world cuttlefish must be present in very large numbers, yet dredging and trawling, the usual methods of investigating the inhabitants of the sea, have been singularly unsuccessful in landing more than a few. This is almost certainly due to their agility in dodging the nets. Nevertheless, they must be plentiful since they form the food of the sperm whale, an’ animal whose appetite presumably takes a lot of satisfying.
From the remains of tentacles found in the stomachs of whales and from trustworthy reports of specimens actually seen that have escaped capture, the largest probably measure up to fifty feet. Possibly individuals larger than this exist, but the bodies of cuttlefish are so soft and fragile that specimens are seldom hoisted aboard whole, even when captured, and those cast ashore are as often as not in a very damaged condition. But fifty feet, or even less, of struggling cuttlefish, with a writhing mass of muscular tentacles, ten, twenty or thirty feet long, each beset with numerous suckers edged with rims of sharp, horny teeth, is sufficiently fearsome for the stories of their greater size to be excusable if not acceptable.