[Illustration: FIG. 26.--_Xenophora_ (_Phorus_) _pallidula_ Reeve. A mollusc which escapes detection by covering itself with dead shells of other species. (From a _Challenger_ specimen in the British Museum, × ½.)] The formidable spines with which the shells, _e.g._ of the _Murex_ family, are furnished must contribute greatly to their protection against fishes, and other predatory animals. _Murex tenuispina_, for instance (see chap. ix.), would prove as dangerous a morsel in the mouth of a fish as a hedgehog in that of a dog. Whether the singular tooth in the outer lip of _Leucozonia_ (see chap. xiv.), a feature which is repeated, to a less marked extent, in _Monoceros_ and several of the West Coast muricoids, is developed for defensive purposes, cannot at present be decided. The _Strombidae_ possess the power of executing long leaps, which they doubtless employ to escape from their foes. In their case alone this power is combined with singular quickness of vision. On one occasion Mr. Cuming, the celebrated collector, lost a beautiful specimen of _Terebellum_, by the animal suddenly leaping into the water, as he was holding and admiring it in his hand. Miss Saul has informed me that the first living specimen of _Trigonia_ that was ever obtained was lost in a similar way. It was dredged by Mr. Stutchbury in Sydney Harbour, and placed on the thwart of a small boat. He had just remarked to a companion that it must be a _Trigonia_, and his companion had laughed at the idea, reminding him that all known _Trigonia_ were fossil, when the shell in question baffled their efforts to discover its generic position by suddenly leaping into the sea, and it was three months before Mr. Stutchbury succeeded in obtaining another. Some genera possess more than merely passive means of defence. Many Cephalopoda emit a cloud of inky fluid, which is of a somewhat viscous nature, and perhaps, besides being a means of covering retreat, serves to entangle or impede the pursuer. The formidable suckers and hooks possessed by many genera in this Order are most dangerous weapons, both for offence and defence. _Aplysia_, when irritated, ejects a purple fluid which used to be considered dangerously venomous. Many of the Aeolididae, including our own common _Aeolis papillosa_, possess stinging cells at the end of their dorsal papillae, the effect of which is probably to render them exceedingly distasteful to fish.