The science of life : fully illustrated in tone and line and including many diagrams

FURTHER PATTERNS OF INDIVIDUALIZED ANIMAL LIFE

Fig. 87. The common Cuttlefish (Sepia).

Wim. Satcwecen.

Above on the right in backward flight ; below, capturing a crab.

a shelter of stones, pouncing out upon unsuspecting passers-by and falling on top of them like a parachute of serpents. In the argonauts, which are closely related to the octopuses, the female carries a delicately built spiral shell, partly in order to protect her own body but chiefly as a sort of perambulator for carrying her eggs. Both octopuses and argonauts have eight long tentacles. The cuttle-fish and squids, however, have ten; they constitute the largest and most varied group of living cephalopods, and swim through the sea like fish, propelling themselves either backwards or forwards by means of fin-like structures that run along the sides of their bodies. Of the ten tentacles two are very long, and are generally kept curled up out of the way, but they can be suddenly shot out to snatch at victims ; the remaining eight are shorter, and are used to hold the prey more firmly once it has been caught. Embedded in the flesh of the back of the squids is a shell homologous with the shells of snails ; in some species the shell is a thin, horny “sea-pen,” and in others it is the white, massive “ cuttle-bone”’ familiar to canary owners. Another kind of cephalopod, the pearly nautilus, is found swimming near the bottom round the shores and coral reefs of the South Pacific—it lives in a beautifully coiled spiral shell, a shell very different in

structure from the perambulator-shell of the female argonaut, and its numerous tentacles are not provided with suckers. The fossils known as ammonites are the spirally coiled shells of a vast parallel group of cephalopods that has long been extinct.

The cephalopods breathe by rhythmically inhaling and exhaling water into and out of a large “ mantle-cavity*’ where it passes over their plume-like gills. By suddenly ejecting water from this cavity they can squirt themselves rapidly backwards ; this is their method of flight from danger. The cuttlefish have an ingenious additional method of evading their enemies, depending upon their astonishing powers of rapidly changing colour—powers that put a chameleon to shame—and upon the inky fluid, sepia, which they can emit when they wish. A closely pressed cuttle-fish tries at first to mislead its pursuers by changing as it flees from white to dark brown, then to a mottled colour and so on. If these devices should fail it has another resource. First it becomes very dark indeed, and for a few seconds remains so. Then abruptly it turns off to one side, escaping in a direction at right angles to its original line of flight ; as it does so it suddenly turns white and at the same time it belches out a puff of sepia, which travels away in the opposite direction. ‘The pursuer, which has

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