Baxter Springs news. [volume] (Baxter Springs, Kan.) 1882-1919, 1893-11-25
AS TO THE ORIGIN OF LUNGS.
True Purpose OF the Fish's Air Bladder
No Use In Swimming.

whose true purpose has long been
classed among the mysteries Of animal
organization. That the bladder was
evolved as swimming organ, or is Of
any essential utility for that purpose,
there is the strongest reason to ques-
ton. As 1t ut present exists 1t is often
too small to be of use in changing the
gravity of the fish, and in many cases,
1t is entirely absent In others its COM
pressing muscles seem incapable Of
being used to expand it Yet in all
these cases the fish seems at no disad-
vantage in swimming as compared with
those that possess large and efficient
bladders As an instance, we may cite
the mackerel, which has no swimming
bladder, and the great shark tribe,
which Is also bladderless.
The bladder varies greatly in size in
closely allied species A like singular
variation occurs in the case Of related
genera Its variations in form are
equally marked Ordinarily it is SIM
pie sac with smooth interior. In some
instances it has a cellular interior, and
in others it is divided by transverse par
titions into from two TO four sections.
In other cases it is divided by longi-
tudinal partition into two lateral
halves. In some families there is re-
markable development of lateral ap-
pendages of varying character. In
others, the internal SPECULATION becomes
SO great that the bladder resembles the
batrachian lung, and evidently does
duty in the breathing of air.
The contents of the bladder differ in
different fishes In fresh water fishes
1t is nearly pure nitrogen. In marine
fishes, on the contrary, oxygen is in
excess. This is particularly the case in
the deep swimmers. in some of which
the bladder has been found to contain
as much as 81 per cent OF oxygen.
These gaseous contents, if obtained
through secretion by the blood vessels,
are not always SO obtained, for In many
fishes an arrangement exists by which
air may enter the bladder from without.
This is what is known as the pneumatic
duct, tubular connection between the
and the air bladder, not un-
like that which supplies the lungs of
This duct presents the
same remarkable variability observed
in other characteristics of the air blad-
der. Its point of connection with the
tract varies, being usually
-, %1a hat in, Hc hac
far back as the stomach. In the CANDID
order of fishes the duct is short one,
and always open. In the Pnysostome
order it is longer, and in many in
stances closed, being occasionally
reduced to a fine flament In the
other orders of Teleostean fishes. which
the great majority of species,
the pneumatic duct does not exist
Whatever function this duct may have
once performed, therefore, it seems as
rule to have lost its utility. That it's
function was an essential one in the
early stages of fish life is rendered evil
dent by the fact that NIL fishes which
have bladder at all possess a pneumatic
duct in the larval stage of growth.
What, then, was its primitive func-
ton? In attempting to answer this
question we must first consider the air
bladder in relation to tn. fish tribe as
whole. In one principal order of fishes
the Elasmobranchs-the air bladder
does not exist No shark or ray pos
sesses this organ. The conditions of its
in the Teleosteans we have
already considered. But in the most
ancient existing order OF fshes-the
which but q few repre-
remain. it exists in an inter-
esting condition. In every modern Ga
mold the air bladder has an effective
duct, which usually opens
into the dorsal side Of the oesophagus,
but in the sub-order Polyterus it opens,
like the windpipe Of living breathers,
into the ventral side. Finally in the
small sub-order of Dipnoi also a sur
vivor from the remote past, the duet
not only opens centrally into the eso-
phagus, but the air bladder does duty
Is lung. Externally it differs IL no
particular from an air bladder. but in
it presents cellular structure
which nearly approaches that of the
Jung of the batrachians.
To the current views l oppose the
natural presumption that the duty
which it observed in the most ancient
ishes was its primitive function The
Iacts of embryology lend strong sup
port to this hypothesis For the air
bladder is found to arise in q manner