Page:Popular Science Monthly Volume 29.djvu/694

676 animal forms, belonging to the Molluscan races, we may discover equally admirable examples of economy in natural work. Among the cephalopods or cuttle-fishes we observe such features. Any one who has seen an octopus resting in its tank in an aquarium must have been struck by the puffing and blowing movements of the sack-like body, the nature of which excited Victor Hugo's imaginative powers in the "Toilers of the Sea." The octopus is seen to inspire and expire with great regularity. The soft body expands and contracts rhythmically enough to excite a natural comparison between its respiratory acts and our own. If we could dye the water so that our eye could follow the currents which the octopus inhales and exhales, we should perceive that at each inspiration the soft body expands, and water is drawn in two currents into the neck-openings. These openings lead directly each into a gill-chamber of the animal. Here, inclosed in its own cavity, we find a plume-like gill. In its nature, this structure is simply a mesh-work of blood-vessels, and thus comes to resemble a lung in its essential features. Impure blood—that is, blood laden with the waste materials of the octopus-body, with the products of the vital wear and tear—is driven into the gill on one side. Subjected to the action of the oxygen gas contained in the water breathed in, the blood is purified. Its waste materials are given forth to the water, and it is passed onward out of the gill on its way to the heart for recirculation throughout the cuttle-fish frame.

Breathing in oxygen entangled in the water is, therefore, in the case of the cuttle-fish, an analogous act to that seen in higher animals, which inhale oxygen directly from the air. The octopus, however, performs an expiratory act likewise. Placed below the head is a short tube, named in zoölogical parlance the "funnel." When cuttle-fish inspiration has come to an end, expiration begins. The body contracts, and the water, which a moment before was drawn into the gill-chambers by the neck-openings, is expelled from the "funnel." The openings of entrance are guarded by valves. These close when expiration begins, and the water has no choice save to find a forcible exit by the tube just named. So far, in octopus existence it would seem as though there was no economy of power exhibited in the act of breathing. Muscular action expands the soft body, and muscular force contracts it. There is exhibited here a plain difference between the octopus and the higher vertebrate.

But the story of cuttle-fish economy is not yet completed. A moment more and your octopus, which sat crouched in the bottom of the tank, is seen to wing its way through the water. It skims like a living rocket through the clear medium in which it lives, as if impelled by some marvelous and invisible agency. The secret of this flight is the solution of cuttle-fish economy and reserve force. So long as the resting-mood prevails, the water used in breathing is ejected slowly, or at least without any marked display of force. But when