326
'
THE sms
'
_
’
like the North Sea it is necessary to be able to tell the age
of great numbers of sh.
Fortunately the plaice carries=
its own age indelibly Written upon it.
Situated in a cavity
just behind the brain are
two small white bones.
These
lie loose in the ear sac and enable the sh to regùlate its
balance in the water, just as the semicircular canals in our
ears
provide us unconsciously with a_means of keeping
ourselves upright (Plate 118).
Examination of these ear
bones, or “ otoliths,” shows that they .possess alternate
'
light and dark Concentric rings, similar in a way to those
onfa crosslseétion of 'a tree trunk.
It has been proved
by a study of the earbones of marked sh that these rings
correspond. to the summer and winter growth of the sh,
Of great importance'in the study of the life—history of a
sh is a“knowledgeof its food and feeding habits.
The
method of nding out the chief food eaten is a very simple
matter and Ïmerely consists in opening the stomach and
examining the contents.
When a very large number of
.
sh have been thus examined over a period” of tWO or three
'
knowledge is gained Of the most common kindof
food for the dierent sized sh and of any changes in the
diet that may occur during the seasons». …Having discovered
the food the next problem is to ndout what its distribution '
is in the sea, because where the food is there we should
.
naturally expect to
the sh that feed on it._
Now, the 'adult plaice is a bottom feeder; that is, it
—
makes its nieals of animals that mostly live ‘on the sea
oor. and while ”very.— many animals are included in its diet,
the most"important item by farfor the adult plaice in the
.
North Sea is a small shellsh known as Spisula (Plate
118).
T0 examine the distribution of this sort of food the
.
grab is used and the actual numbers of animals caught in a
_
given area counted, so that, by making observations at '
stated intervals over a large region, a chart may be drawn
'
THE sms
'
_
’
like the North Sea it is necessary to be able to tell the age
of great numbers of sh.
Fortunately the plaice carries=
its own age indelibly Written upon it.
Situated in a cavity
just behind the brain are
two small white bones.
These
lie loose in the ear sac and enable the sh to regùlate its
balance in the water, just as the semicircular canals in our
ears
provide us unconsciously with a_means of keeping
ourselves upright (Plate 118).
Examination of these ear
bones, or “ otoliths,” shows that they .possess alternate
'
light and dark Concentric rings, similar in a way to those
onfa crosslseétion of 'a tree trunk.
It has been proved
by a study of the earbones of marked sh that these rings
correspond. to the summer and winter growth of the sh,
Of great importance'in the study of the life—history of a
sh is a“knowledgeof its food and feeding habits.
The
method of nding out the chief food eaten is a very simple
matter and Ïmerely consists in opening the stomach and
examining the contents.
When a very large number of
.
sh have been thus examined over a period” of tWO or three
'
knowledge is gained Of the most common kindof
food for the dierent sized sh and of any changes in the
diet that may occur during the seasons». …Having discovered
the food the next problem is to ndout what its distribution '
is in the sea, because where the food is there we should
.
naturally expect to
the sh that feed on it._
Now, the 'adult plaice is a bottom feeder; that is, it
—
makes its nieals of animals that mostly live ‘on the sea
oor. and while ”very.— many animals are included in its diet,
the most"important item by farfor the adult plaice in the
.
North Sea is a small shellsh known as Spisula (Plate
118).
T0 examine the distribution of this sort of food the
.
grab is used and the actual numbers of animals caught in a
_
given area counted, so that, by making observations at '
stated intervals over a large region, a chart may be drawn