The shell of this genus does not contain the animal, as in Nautilus, but it is enveloped in two flaps of the mantle, at the posterior part of the animal, the shell being concealed with the exception of a part of the edge on each side. The body of the animal is long and cylindrical and the arms are quite short, more nearly resembling those of the Nautilus than those of the Octopus or squid. The body ends in a disk which is supposed to be a kind of sucker, by which the animal can adhere to rocks, thus enabling it to freely use its arms in obtaining food. It has been supposed by some anatomists that the shells of the fossil Ammonites were attached to the animal in a similar manner, and if this should be true these small mollusks would assume a new meaning as being the last survivors of a large group of animals of which all except Spirula are extinct.

Probably the best known of the shell-less cephalopods is the octopus, with its rounded body, large eyes and long arms. Almost everybody has read Victor Hugo's weird account of the octopus in his "Toilers of the Sea," and the animal has thus been rendered more or less familiar, although it was made to do several things, by the author that it would not do in nature, as, for example, "drinking" a man alive, The Octopus is found abundantly throughout temperate and tropical seas, generally on the coast among rocks, but frequently on the sandy bottom in water of moderate depth. Here it may occasionally be seen "walking" clumsily along on its eight long arms, its little round body being balanced above the arms. Its favorite position, however, is among the rocks. In such a locality it will squeeze its body into some crevice and spread out its arms until they form a sort of web, resembling in this position a huge spider waiting for its prey. And it may well be likened to a spider for from this web there is no escape if once a hapless fish has come in contact with the powerful suckers on the long arms. The poor fish is paralyzed when seized by the octopus and is drawn towards the mouth, where it is torn to pieces by the beak-like jaws, and swallowed.

Like many of the mollusks of which we have written the octopus is esteemed as a valuable article of food by several savage tribes as well as by some civilized people. The native of the Pacific coast catches the Octopus (Octopus punctatus) by a very ingenious method. Providing himself with a spear twelve or fourteen feet long which has four or five barbed pieces of hard wood some fourteen inches long attached to the end, he paddles his canoe to the feeding ground of the mollusk. One is soon found in ten or twelve feet of water and the Indian carefully lets down his spear until within a few inches of the center of the animal, when he quickly plunges it into the soft mass. Instantly the water is in commotion, the eight long arms writhing about in an endeavor to reach the boat. The Indian knows that should this happen his chances for life would be slim indeed. But he is prepared, and carefully lifting up the octopus with his barbed spear until it is above the surface of the water, he plunges a long, sharp spear, with which he is provided, into each arm where it joins the body. At each plunge of the spear, an arm becomes helpless and in a short time the animal, which but a few moments before had the power of a score of men, lies in the canoe, a shapeless, helpless mass.

That the octopus is good eating the writer can attest from experience, for during a visit to Yucatan some years ago this mollusk was served as a meat dish and was very palatable, the flesh being firm and tender and much resembling chicken. The portion which fell to the writer was the head, with a part of the arms attached.

One of the most interesting characteristics of the Octopi and allied cephalopods is their facility for changing color when danger is near. These changes are caused by little pigment cells just beneath the skin, which expand and contract. Thus, if a person is looking at an octopus in captivity and the animal is so placed that it cannot escape, the observer will be astonished to see the body of the animal suddenly assume a deep pinkish color which in turn is succeeded by a blue and then by a green, and finally a return to pink. The body is covered with these little pigment cells, the different colors — pink, blue and green — being so evenly scattered over the surface than when each color cell is expanded the whole body assumes that tinge. This is one of the most wonderful characteristics of the Mollusca.