New-York daily tribune. [volume] (New-York [N.Y.]) 1842-1866, 1847-10-28

what have said Of the rsdats as the differences
between the two large types Is less In the details
OF their organization, than IN the mode Of the ar
rengeuent Of their organs. The rsdista have their
organs distributed around the centre. This centre
IS the mouth, and the mouth 10 turned either up
ward. We have the mouth upward in the pO-
lypi downward ia the echinodermata Nowhere
have we the mouth on the anterior portion OF the
body. Among the radata there IS no anterior ex-
tremity which prevails over the sides OF posteriOr
extremity. All the rays diverge from the centre
and are Of equal value, and when We can trace
some indications ola bllateral symmery il is owing
only TO slight differences between these rays, and
hot owing to any general arrangement on the two
sides OF longitudinal axis There IS no Ongituci-
nal axis proper ia the radiata-
In the mOlusca we have an entirely different ar
rangement. The mouth moves toward one end Of
the animal and now We have al anterior extremity,
though we have not yet head-not organs Of
sense placed always round the head. But there
is at least anterior extremity on which the mouth
IL situated, and round 1t there are tentscles by
which the food il introduced into the alimentary
canal Thus the anterior extremity s given by the
position OF the mouth, and the two sides by
the general arrangement OF the viscera- We
have not only an anterior extremity but we have
dorsal region, a right and a lett-hsnd side
q lower and an upper regiOn-and IN all the mol
lusca those regions can be readily distinguished,
though the animal does not always stand on the
lower extremity. There some who for their
whole lives rest on one side. For instance, the
oy ster lives constantly lying the left-hand side
others are attached by the upper extremity and
stand the lower extremity upward, and II Is only
by means OF comparison that we can ascertain
which is the right and left hand and by finding
where the mouth is placed and by examining the
relative position Of the different internal organs
The body Of the mousca is always very soft
Hence their name mousca, which signifies soft
animals" The body is exceedingly coniractile.
IL can be contracted so much that large animals
will occupy very small space when contracted.
For instance, the animal which forms this she'll
which 10, as you perceive OF large size, and out OF
which il pushes large foot on which It walks
when contracted is entirely concealed in the bot
tom OF the cavity. In others there are two shells
which cover the soft parts. Sometimes there's but
one shell very much curved on itself and IN other
cases forming only fiat disc. covering only the up
per part of the body.
The softness OF these animals "a very character
istc, and in no other type do We lind tissues so
soft as in this class and so capable OF containing
great quantity Of water. They continually absorb
certain quantity Of water which penetrates the
mass Of the body and maintains it in a state Of ex
pansion. But when contracting this water. is ex-
pressed In way quite similar 10 the water con
tanned In the sponge when It II squeezed.
The organization OF the molusca is, in some
cases highly complicated. In others 1t is as simple
almost in the poypi. The difference In the latter
case is only in the symmetry The mouth being in
the anterior region. and the nervous system sur
rounding the anterior extremity of the intestIna al
canal in a vertical position, while In the radiata
the nervous system is placed horizontally. The
nervous system is placed above the intestinal ca
nal forming ring around the tube with some other
ganglia below, from which the nervous threads run
into the different organs. From the upper glanglion
we have nervous threads going into the tentscles
L IL t.,t affha ms
in the cavity Of the animal and here are threads
running into the muscular hbres which move the
animal similar structure is found IN those hav-
ing two valves only the symmetry Is somewhat
different Always the nervous system is composed
only of a swelling above and cling below the al
imentary canal from which the threads are sent 10
the different organs That is the general arrange
ment Of the nervous system in all the molinsca
the alimentary tube passing through the nervous
ring, but the ring having vertical position, while
in the radista it has a horizontal position
We see the difference here is rather in the posi-
ton OF the organ-ln the relation with other parts
than in the structure. This nervous system is
scarcely any more complicated than the nervous
system of the star-fsh, or echina. Perhaps these
ganelia somewhat larger and less numerous;
and In the smaller number is evlnced a degree OF
superiority. We see in the higher animals that
certain organs not unique but In pairs In the lower
animals exist in great numbers In the star fishes
eyes we have an eye at the end of each ray-as
many eyes there are rays, and as many ganglia
as there rays and from each a nervous hlament
running through each ray Here we have small
er number OF nervous ganglia and they are placed
so that stands above the other and on the ante
ror region Of the animal in that way this ganglia
or nervous centre has greater influence upon the
whole animal and it is only owing TO the position
of that that the anterior region OF the
animal has become more important and possesses
greater vitality while other organs rOundthe mouth
have higher Importance 20 the functions OF hie
Wherever the nervous system becomes larger and
acquires a preponderance over the other organs,
then we see that life acquires greater intensity
and that all the important organs are accumulated
1t is So with the head of vertebrated animals which
contains all the organs Of any high Importance
The organs in other parts OF the body Just as i'm
por,snt 70 the maintenance OF life and the sound
condition OF the animal, nevertheless they do not
possess the high value which the organs IN the
head Of these animals exhibit.
The alimentsry cavity Is complicated in the mol
lusca 1t is longer simple branched sac, as 1t
is in the radiats- But We have in them, behind
the mouth, which is usually surrounded by ten
tacles ~ introduce the food sometimes two 10
number and sometimes four arranged in pairs,
two above. two below, or only two on the sides
behind the mouth. was about 10 say, there is
narrow tube. the gsophagus, and usually large
Now this stomach is complicated inasmuch as
there is live, glandulsr organ united with II
and this liver is sometimes very large, surround
ing the whole stomach and secretiDg greenish
dark liquid, known under the name OF bile,
which is introduced into the stomach and helps d.
geston. This bile the secretion OF the liver 10 very
in all the mollusca The liver Is some
times large as exceed in size the whole of the
animal IL is more than half the weight of the
body. Sometimes there are several livers, two,
three or four arranged around the stomach and
opening directly into it.
rhe organs OF respiration are always distinct,
and uniformly present the form OF giils Their po
,ition varies very much in the molluscs, and
will not now enter into the details OF the arrange
nent OF these respiratory organs, as shall have
occasion u ex plain the differences which they ex
hbt in different types Of the great group OF mous
ca But every where these gllls are present and
when say everywhere, do not exclude that class
which breathe the atmospheric air, which have no
lungs, notwithstanding they resplre by air, but
have gills like other mollusca, only they are kept
in contact with atmospheric air and not with water
Their gilis then. are not al all similar u the lungs
n higher animals, and are entirely similar 70 the
sills Of other mollasca- What are gills Every |
where q blood vessel divides into parallel branches
which are brought into oontsc. with the air con
.sined either in the atmosphere or in the surround