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The semi-transparent squids, with posterior triangular fins, swim back and forth as delicately poised as submarine monoplanes. When a live fish is placed in the water the squid darts at it, grasps it firmly with the suckers or the tentacles and cuts off the head, eating only the body. The cuttlefish, with broader body, striped like a zebra, and big elephantine head, constantly undulates a fin-like fringe around the border of its mantle, as it nervously drifts here and there. Frequently it wriggles into the sand which it throws upon its back, or, if much disturbed, ejects a cloud of ink in which it disappears. The large octopus has a body that suggests both a toad and a spider, with highly developed eyes and brain projecting above it. Generally this devil-fish lies sleeping in a corner of the rocks, or lazily reaching out and creeping about by means of eight long tentacles that express a giant's strength. With a spurt of water from its siphon the octopus may dart rapidly through the tank, and by directing the tube of its siphon, go whither it wills. Lying upon the bottom of an open trough, often buried in the sand, is the very interesting electric ray. If one presses the fingers upon the broad body where it runs into the tail he will, in the words of a Cook's guide, "get a strike." The electric tissues are descended from muscle fibers which in the course of evolution have come to produce electricity instead of motion. In the embryo ray the primitive muscle cells first appear, then they swell out anteriorly and shrivel up posteriorly until each loses the characteristic striated muscle structure and becomes an electric plate lying in a little compartment embedded in a jelly-like substance. Electricity is produced by some chemical action upon innumerable minute granules stored up in the protoplasmic network pervading the electric plates. The shock