202
'
THE SEAS
live in m_ud, spending their days slow1y ploughing through
it, sÿvallowing, as they go, large quantities from which they
extract such nourishment as it contains, just as the earth—
worms
do on land.
The burrowing sea urchins feed in
somewhat the same manner, but they pick up particles by
means of special grasping tube-feet, _which surround the
mouth. Other animals of which the Shipworm is an ex—
ample, obtain their food by boring ; while others again scrape
off the various plants and animals which form a crust over
the surfaces of the rocks.
Of the latter type of feeders, the
common sea urchins are examples, they hold on to the rock
with their tube feet and bite off the food by means of ve
‘
long teeth, which are supported in an intricate skeleton
known, on account of its discoverer and shape, as Aristotle’s
which is shown in Plate 79.
The muscles of the
'
force the teeth downwards so that they all come
.
together beneath
biting off a
of
food, which is automatically pushed into the mouth.
Other animals WhlCh scrape their food from the surface
of stones are the common shore snails, such as the peri—
crawl aboutby means of their
big
In commonwith other members of the
pos-'sesS a_- very characteristic feeding
apparatus-consisting of a long horny ribbon, made up of
.
_many rows' of ne teeth, and known as the “ radula ”'
-
:
-'
=
or lingua] bbon (Fig. 44).
This is _supportedby astrength—
eningframework over Which it-,is
_
bac—kwards and
forwards like a.rope over a pulley. The whole mechanism
'
canbe withdrawn into the mouth wheri the» animal is not
feeding, but when in use is pushed out against the food
which it rasps away by continuous backward and forward
_
movements, each piece being pullèd back into the m0uth
:
and further broken -up by the help of jaws before it is
_
_
'
swallowed.« The rad-ula is.constantly being worn away, but
'
THE SEAS
live in m_ud, spending their days slow1y ploughing through
it, sÿvallowing, as they go, large quantities from which they
extract such nourishment as it contains, just as the earth—
worms
do on land.
The burrowing sea urchins feed in
somewhat the same manner, but they pick up particles by
means of special grasping tube-feet, _which surround the
mouth. Other animals of which the Shipworm is an ex—
ample, obtain their food by boring ; while others again scrape
off the various plants and animals which form a crust over
the surfaces of the rocks.
Of the latter type of feeders, the
common sea urchins are examples, they hold on to the rock
with their tube feet and bite off the food by means of ve
‘
long teeth, which are supported in an intricate skeleton
known, on account of its discoverer and shape, as Aristotle’s
which is shown in Plate 79.
The muscles of the
'
force the teeth downwards so that they all come
.
together beneath
biting off a
of
food, which is automatically pushed into the mouth.
Other animals WhlCh scrape their food from the surface
of stones are the common shore snails, such as the peri—
crawl aboutby means of their
big
In commonwith other members of the
pos-'sesS a_- very characteristic feeding
apparatus-consisting of a long horny ribbon, made up of
.
_many rows' of ne teeth, and known as the “ radula ”'
-
:
-'
=
or lingua] bbon (Fig. 44).
This is _supportedby astrength—
eningframework over Which it-,is
_
bac—kwards and
forwards like a.rope over a pulley. The whole mechanism
'
canbe withdrawn into the mouth wheri the» animal is not
feeding, but when in use is pushed out against the food
which it rasps away by continuous backward and forward
_
movements, each piece being pullèd back into the m0uth
:
and further broken -up by the help of jaws before it is
_
_
'
swallowed.« The rad-ula is.constantly being worn away, but