_
130
THE SEAS
they should be able to maintain the level at which they are
drifting.
The means by which this capacity is attained are '
many and varied, the general aim being to reduce the
organism’s specic gravity directly until it is the same as. o‘r
less than, that of the surrounding sea water, or to obtain a
similar effect in a more indirect manner.
.
Species that have achieved the power of becoming lighter
than water are comparatively few in number.
The chief
examples occur in a group of jellyshes known as Siphono—
‘
phores. - The name of the Portuguese Man—o’-War, a
stinging jellysh, is well—known to all.
This
animal
'
possesses a specially designed
“
oat ” into which gas _is
secreted by a specialized gland.
This gas—lled reservoir
'
”projects above the surface of the sea and acts -as a sail, by
_
means
of which the wind blows the jellysh along, transporting it from place to place with tentacles extended in all
directions ready to seize any unwary prey that they may
_
.
touch, instantly paralysing it with their batteries of stinging
’
cells.
Another closely allied form is the Velella, or “
By
the wind Sailor ”
(Plate 50).
This likewise has a small
‘
gas-lled sail.
The animal; when seen ali—ve, is of a fairy—
_
like delicacy, - possessing this transparent, papery sai},
situated above the centre of the body :
on
the under
_
surface is the “
centrally placed and surrounded by
delicate mobile tentacles of a sky—blue tint. These little
creatures, which reach a size of one or two inches in length,
are nat‘iVes of the warrher ocean waters and the Mediter—
ramean.
However, they are occasionzilly to be found '
strarided along the western and south—western shores of
.
the” British Isles after prolo'nged southerly winds, that have
waited them speedin along the surface of the sea from the
warme'r latitudes; —
—.
_
'
.
'
In orderto_reduce the specic gravityxas nearly as possible -
,
to that of.seà;: water;_ many animals make‘ use of tats and =
130
THE SEAS
they should be able to maintain the level at which they are
drifting.
The means by which this capacity is attained are '
many and varied, the general aim being to reduce the
organism’s specic gravity directly until it is the same as. o‘r
less than, that of the surrounding sea water, or to obtain a
similar effect in a more indirect manner.
.
Species that have achieved the power of becoming lighter
than water are comparatively few in number.
The chief
examples occur in a group of jellyshes known as Siphono—
‘
phores. - The name of the Portuguese Man—o’-War, a
stinging jellysh, is well—known to all.
This
animal
'
possesses a specially designed
“
oat ” into which gas _is
secreted by a specialized gland.
This gas—lled reservoir
'
”projects above the surface of the sea and acts -as a sail, by
_
means
of which the wind blows the jellysh along, transporting it from place to place with tentacles extended in all
directions ready to seize any unwary prey that they may
_
.
touch, instantly paralysing it with their batteries of stinging
’
cells.
Another closely allied form is the Velella, or “
By
the wind Sailor ”
(Plate 50).
This likewise has a small
‘
gas-lled sail.
The animal; when seen ali—ve, is of a fairy—
_
like delicacy, - possessing this transparent, papery sai},
situated above the centre of the body :
on
the under
_
surface is the “
centrally placed and surrounded by
delicate mobile tentacles of a sky—blue tint. These little
creatures, which reach a size of one or two inches in length,
are nat‘iVes of the warrher ocean waters and the Mediter—
ramean.
However, they are occasionzilly to be found '
strarided along the western and south—western shores of
.
the” British Isles after prolo'nged southerly winds, that have
waited them speedin along the surface of the sea from the
warme'r latitudes; —
—.
_
'
.
'
In orderto_reduce the specic gravityxas nearly as possible -
,
to that of.seà;: water;_ many animals make‘ use of tats and =