SHELL-FISH, OR MOLLUSCS 



341 



yet another most effective locomotive organ. This is the so-called funnel, or siphuncle, a 

 membranous tube connected with the capacious gill-cavity which is formed by a folding of the 

 mantle on the under-surface. When at rest or moving leisurely, the water taken in through the 

 pocket-like entrance to this cavity is discharged through the funnel without any particular 

 effort. The animal can, however, at will leave go its attachment to the rocks, and propel 

 itself swiftly through water by successive forcible expulsions of the water through the funnel. 

 By directing the aperture of the funnel to the right or left, the creature can also direct its 

 course in whatever direction it desires. When thus swimming, its translation is necessarily 

 backwards. Another notable feature of the octopus is the " ink-bag," a huge gland secreting 

 an inky-black fluid, which, as produced by the common cuttle-fish, constitutes the sepia of 

 commerce. The contents of the ink-bag are discharged through the funnel at the will of the 

 animal ; as soon as the ink is brought into contact with the water, it becomes distributed 

 through it in the form of a thick cloud, under cover of which the mollusc makes good its 

 escape from any attacking enem)-. 



The octopus in British seas by no means attains to its ma.ximum growth. E.xamples with 

 arms from 2 to 2| feet in length are accounted large specimens. In Mediterranean waters, 

 however, these dimensions are much exceeded, individuals with arms 5 feet long, which are 

 capable of covering a circular area no less than 10 feet in diameter with their fully extended 

 appendages, being frequently recorded. In the West Indies, on the North-west American coast, 

 and also in Chinese seas, similar, if not larger dimensions are attained by these creatures. 

 That these monster octopods, or " devil-fish," as they are sometimes designated, prove a source 

 of danger to human life has been abundantly demonstrated. Lurking, as is their custom, 

 among rock-crevices, they seize hold of any moving object which approaches within reach of their 

 extended arms. Bathers in this manner have been seized and drowned, it being impossible for 

 even the strongest swimmer to free himself from the clutches of one of these animals, which, 

 while retaining a firm hold on the rocks with a portion of its hundred-suckered arms, has 

 entwined the others around its victim. 



The natural food of the octopus are crabs, lobsters, aud their like; and in places like 

 the Channel Islands, where the tide retires very 

 low, leaving the rock-fissures inhabited by the 

 molluscs more or less exposed, their presence may 

 be often foretold by the accumulation of empt}', 

 broken-up crab-shells around the entrances to their 

 retreats. In common with other members of its 

 tribe, the octopus is furnished with a strong, horny, 

 parrot-like beak, wherewith it can with ease break 

 through the shells of its accustomed food. The 

 year 1900 was remarkable for the extraordinary 

 abundance of the octopus on the English south 

 coast, the result of their collective depredations 

 very seriously affecting the local crab and lobster 

 fisheries. The pots laid down over-night, in place 

 of yielding the following morning their customary 

 quota of marketable crustaceans, were more often 

 than otherwise found to contain nothing but 

 broken-up shells and a loathsome " devil-fish." 



The Squids and Cuttle-fishes, with their 

 large lustrous eyes, are especially adapted for an 

 open sea life, and for this purpose are furnished 

 with lateral fin-like membranous expansions. A 

 more important structural distinction is their pos- 

 session of two supplementary appendages, which, 



Phoio »> II'. S^v,II,-Ktn<, F ZA. 



SHELL OF THE PEARLY NAUTILUS 



The inner lining of this shtil is briliianily iridescent 



