It is not my intention to formally portray the anatomy of the Octopus,—the nature and uses of its various organs will be sufficiently indicated in the course of my remarks,—but before giving an account of its life-history and habits, I will briefly describe its affinities, and the position it occupies in the scale of Nature.
One of the great primary groups or divisions of the Animal Kingdom is that of the soft-bodied Mollusca; which includes the cuttle, the oyster, the snail, &c. It has been separated into five “classes,” of which the one we have especially to notice is the Cephalopoda,[3] or “head-footed,”—the animals belonging to it having their feet, or the organs which correspond with the foot of other molluscs, so attached to the head as to form a circle or coronet round the mouth. Some of these have the foot divided into eight lobes, and are therefore called the Octopoda:[4] others have, in addition to the eight feet, lobes, or arms, two longer tentacular appendages, making ten in all, and are consequently called the Decapoda.
Of the ten-footed section of the cephalopods, there are four “families”; two only of which exist in Britain—the Teuthidæ, and the Sepiidæ. The Teuthidæ are the Squids, or Calamaries, represented by the long-bodied Loligo vulgaris, that has along its back a gristly, translucent stiffener, shaped like a quill pen; from which and its ink it derives its names of “calamary,” “pen-and-ink fish,” and “sea-clerk.” The Sepiidæ are the Cuttles; as a type of which we may take the common “cuttle-fish,” Sepia officinalis, the owner of the hard, calcareous shell often thrown up on the shore, and known as “cuttle-bone,” or “sea-biscuit.”
Of the eight-footed cephalopods,—the Octopoda,—there are two families; namely, the Octopidæ, and the Argonautidæ. The first only is found on our coasts. The British members of it are the common Octopus, O. vulgaris, and the Eledone, E. cirrosa, a genus chiefly distinguished from the octopus by its having only one row of suckers, instead of two, along its arms or feet. The Argonautidæ, which inhabit warmer seas than ours, and approach no nearer to us than the Mediterranean and Adriatic, are represented by Argonauta argo, the “Paper Nautilus,”—so called from the peculiar texture of its shell, and the similarity of its shape to that of the true Nautilus, N. pompilius, from which, however, it differs greatly in organisation.
All of these four “families” have two plume-like gills,—one on each side—and are therefore placed by Professor Owen in the “order,” Dibranchiata. To this order belong also the extinct Belemnites, and the still living Spirula, only one entire specimen of which has ever been obtained, and that was in New Zealand, though its beautiful internal shells are sometimes thrown up on the shores of Devon and Cornwall.
The Tetrabranchiata, or four-gilled cephalopods, are represented by a single living genus—the Pearly Nautilus, N. pompilius,—but in Silurian times by 34 genera, and more than 1400 species.[5]
The following diagram will help to explain the relationship of the Octopus to the rest of the cephalopoda.
