THE MANTLE-COVERED ANIMALS. 
127 
bone. Its mantle covers the body and forms a ring 
round the neck, often fitting so closely that its edge 
can only be seen where there is a hole for taking in 
water. In a fold of this mantle are hidden the gills, 
and a short funnel (si, Fig. 49) sticking out of its neck 
is a tube for shooting out the refuse water which has 
been taken in at the mantle-rim. Here we have the 
secret of the rapid movements of the octopus, for, by 
taking in a supply of water at the rim of his mantle 
and sending it out in jets through the funnel, he shoots 
Fig. 49. 
Octopus shooting backwards through the water. 
si, Siphon ; a, arms ; s, suckers on the arms ; e, a bunch of eggs 
of the octopus. 
himself backwards just as a boat is sent through the 
water by a stroke of the oar. Nay, more, if he is 
flying away from an enemy he has an additional 
mode of defence, for within his body is a gland which 
secretes an inky fluid, and this he squirts out through 
the funnel, making a thick dark cloud behind him 
which baffles his pursuer at the same time that it 
helps himself to dart away. 
