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 e.xpulsions 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 enemy. 
The octopus in British seas by no means attains to its maximum growth. Examples 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, and 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 empty, 
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 e.xtraordinary 
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- SHELL OF THE PEARLY NAUTILUS 
session of two supplementary appendages, which. The inner lining of thh Ml U brilliantly iridescent 
