Fig. 322. Octopus macropus (Risso).
Fig. 323. Octopus brevisses (D'Orbigny). Fig. 324. Octopus horridus (D'Orbigny).
The Decapoda are of all sizes. Dr. Grant describes the body, or mantle, of Sepiola vulgaris, found on our coast, as measuring about six lines in length, and as much in breadth, while the head measures four lines in length, and, from the magnitude of the eyes, must be equal in breadth with the body. In Onychoteuthis, distinguished for its uncinated suckers, they are found of the size of a man. In Cook's first voyages, the naturalists to the expedition, "Banks and Solander," to quote Professor Owen's account, "found the dead carcase of a gigantic species of this kind floating in the sea between Cape Horn and the Polynesian Islands, in 30° 44' S. lat., and 110° 10' W. long. It was surrounded by sea birds, which were feeding on its remains. From the parts of this specimen which are still preserved in the Hunterian Museum, and which have always strongly excited the attention of naturalists, it must have measured at least six feet from the end of the tail to the end of the tentacles."
In the genus Eledone the arms are reunited at their base by a very short membrane, with only a single row of suckers. The two best-known species of this group inhabit the Mediterranean. The one is Eledone moschatus, known in Italy under the name of Muscardino, from the strong odour of musk which it emits, even after death and desiccation; the other is Eledone cirrhosus, a small species, bluish-grey on the back, and whitish under the belly.
The habits of Eledone moschatus have been carefully studied by M. Verany. The able naturalist of Nice preserved many of these animals during a month, in a great aquarium, noting their habits. When in a state of tranquillity, the Eledone clung to the sides of the glass tank in which it was kept. Its head is then inclined forwards, with the sac hanging behind; the locomotive tube, turned upwards, presents the orifice between the arms. In this state the animal is yellowish in colour, its eyes dilated, its inspirations regular. But if irritated, a remarkable change takes place: its body assumes a fine maroon colour, and it is covered with numerous tubercles; the eye becomes contracted, a column of water is forcibly ejected from the locomotive tube at the aggressor, and the respiration becomes precipitate, jerky, and irregular. The creature would take a strong inspiration, and, having collected its force, suddenly throw a jet of water to a distance of more than three feet. This state of passion, which the slightest touch is sufficient to produce, endures for half an hour or more. When it ceases, the animal resumes its form and primitive colours; but the least shock impressed on the water is sufficient to give it a deeper tint, which passes like a flash of lightning over the skin of this singular proteus.
The Eledone sleeps by day as well as by night, attaching itself in its sleep to the walls of its prison, leaving its arms to float around, the two inferior ones extending backwards, and the sac inclining over them; its eyes are then contracted, and in part covered by the eyelids. Its respiration is regular and slow, and any ejection of water very rare; its colour is then of a livid grey, and vinous red below, with whitish spots, while the brown spots have now entirely disappeared. While still asleep, it is watchful and attentive to all the dangers which could surprise it. The extremities of the arms floating round its body are ready to announce the approach or contact of any other object. Even the most delicate touch is perceived immediately, and it shrinks from the hand which seeks to approach. Under every circumstance the Eledone exhales a strong odour of musk, which it preserves long after death.
When the Eledone swims, which it rarely does unless pressed by some urgent necessity, it carries the sac in advance, the arms floating behind—the six upper ones being on a horizontal line, the two others approaching each other below. Thus arranged, it presents, in consequence of its flattened form, a very large resisting surface to the water, its progress being due to the alternate dilatation and contraction of the body, which expels the water through the locomotive tube, and by reaction produces a rapid and jerking movement. Sometimes the arms aid the movement; the eyes of the animal are then much dilated, and its colour a clear livid yellow, finely shaded with red, and covered with bright spots.