140 THE OCEAN WORLD. 
we find a great cavity, which opens from within, near the base of the 
capsule ; to the inside of this cavity a second muscular sac is attached 
all round the opening of the capsule, in such a manner that the 
opening leads directly into the cavity of the sac. This cavity conceals 
in its interior a long filament usually rolled up in a spiral, as illus- 
trated in Fig. 48, where the two urticating capsules of the stinging 
apparatus of Physophora hydrostatica are represented, one of them 
being a section, magnified by twelve diameters. This spirally 
rolled-up filament consists of a large quantity of very small, hard, 
sabte-shaped, corpuscular bodies, supported the one against the other, 
and having their points turned inwards. These objects Vogt terms 
“urticant sabres ;” the extremity of the filament consists of curved 
corpuscles, larger, of a brownish yellow, very strong, and with a 
double point. M. Vogt had also opportunities of observing the 
action of these stinging capsules. He has seen them burst naturally, 
and he has also obtained artificially the same result. In the former 
case the filament issues from the opening left at the base of the 
capsule with a sort of explosion. “The use,” he says, “ of the fishing- 
lines becomes evident when we see a Physophora in repose in a vase 
large enough for its full development ; then it takes a vertical position ; 
the lines elongate themselves more and more, by unfolding one by 
one the secondary lines with stinging capsules, and the Physophora 
now resembles a flower posed upon a tuft of roots, with extremely 
long and delicate rootlets reaching to the bottom of the vase. But in 
the case of the Physophora the living roots are in continual motion. 
Each line is elongated, foreshortened,.and contracted in a thousand 
ways. The least movement of the water causes the stinging capsules 
to be suddenly drawn up, the lines hauled in most rapidly being those 
near the crown of tentacles. This continuous play of the lines has 
no other object than to attract the prey destined to feed the polyp, 
and we cannot find any better comparison for them than the fishing- 
lines to which they have been compared. The moment that some 
small microscopical medusz, larva, or crustacean, come within the 
sphere of those redoubted lines, it is at once surrounded, seized, and 
led with irresistible force towards the mouth of this polyp bya gentle 
and gradual contraction of the line; the stinging organs, complicated 
as we have seen them to be in the Physophora, thus serve the same 
purpose as the stinging organs disposed on the arms of the Hydra, 
or on the external surface of the tentacles and prolific polyps of the 
Velella. 
Let us finally note among the Physakne—a family it will be 
recollected of Physophoride—a form which has attracted great 
