138 THE OCEAN WORLD. 
“firm, compact tissue. They are attached obliquely and alternately 
upon a common axis, presenting an exterior curvature, a round 
opening, furnished with a fine, muscular, and very contractile limb, 
and arranged like the iris of the eye. Their power of resistance is 
increased by certain horny hollow threads, which are in direct com- 
munication with the cavity of the vertical axis, and have their origin 
in a common circular canal. 
“The animal,” says Vogt, “is enabled to guide itself in any 
direction by means of the swimming apparatus or air-bags. These, 
on opening, are filled with water, which is again ejected in the 
contractile movement, for their movements may be compared to that 
of the umbrella of the Medusez. It is the violent expulsion of this 
liquid which enables the animal to advance diagonally through the 
water, a kind of motion which is the consequence of its organisation ; 
for where both rows of air-bags are working in the direction of the 
axis of the stem, the organism will incline to the side which works 
most, but always in such a manner that the aérial vesicle will be 
borne forward.” 
In its lower parts the stem expands, becomes flat, and winds itself 
in a spiral. It is hollow, and encloses a transparent viscous liquid, 
in which very small granules are observed, which appear to be the 
result of digestion. ‘To this are attached three different sorts of 
appendages. We shall first address ourselves to the tentacles. 
These form a crown or bundle of vermiform appendages, of a 
reddish colour, over an inch in length, and which are kept continually 
inmotion: these are formed of a glass-like cartilaginous substance ; 
they are conical tubes, closed on all parts except at the point where 
the tentacle is attached to the disc. Their cavity is filled with the 
granulous liquid already mentioned. On the under surface of the 
disc, and to the inside of these tentacles the polyps and fishing-lines 
are attached. 
The anterior part of the polyp is formed of a glass-like substance, 
which changes its form in the most varied and surprising manner. It 
bears a roundish mouth at its summit. In its posterior part the 
polyp presents a straight hollow stem, of reddish colour ; but near to 
this red stem we find a thick tuft of cylindrical appendages, from the 
middle of which spring the extensible and contractile filament which 
Vogt calls the jshzng-lines (fil pécheur), and of which he has given 
the following very strange account :— 
“‘ Each of these appendages consists of an assemblage of cylindrical 
tubes somewhat resembling and analogousto the filament of a Conferva. 
All these tubes are traversed by a continuous canal, which originates 
