ECONOMY OF THE BODY—I
'127
Ganoids and Dipnoi have both and many Teleosts have
neither.
The fact is, that weknoWtoo little about the origin
of these organs.
It. is said, for‘
that'the liver and
pancreas are outgrowths from
mesenterÇn (primitive
gut) and that the liver is the homologue—”of the simple’isac'
.
found in AmphioXus. So far—as the Teleosts are concerned,
one may doubt this derivation ; in such a5case thére
It “seems more 5.probable,—j
that the liver and pancreas arise
the hypoblasttcells'
of the embryo which are actively engaged inconvertirig the
yolk—food before' the 'gut is formed. ' The pyloric cæca,
"
on the other hand, do not develop till much later,
it is
possible that they arise in the samemanner as that suggested
forthe air—bladder, from—the ‘ac(:umulation of Small
'
globules
of air or gases at the Spot where the digestive tract alters
.
—its straight course and makes a _bend ; latér,the duodenum
is formed at this
The pyloric cæca may be correlated'
—
with the pancreas, as some have thought, in so far as their
,
growth iterfereâ with the growth of" the latter and, perhaps
'
,
leads toits di8pe'rSal. ._
'
,'
,
,
'
,
fîîz;yïÎCiRéULÇA“TIoN' A'Nb RESPIRATION,
,
'
'
‘5ï*
aCtiVities ”off digestion 1 and
Within
the organism Would be of _litt—leavail_
present to convey the products from "one place to another.
Onthe one hand, the alimentary Canal is like a retort in which
the most intricate chemical processes we know of, are
constantly reducing the food to a brew suitable for transport
,
through the membranes. On the other hand, the living
tissues are something more than a sieve permitting the
of ”the diss‘olved constituents ;
active cells are
present'selecting the different elements and conVeying them
bloodor lymph (leucocytes), Whilst others arè,busy
removing the ‘ harmful ingredients
,
are two Channels f0r the circulation of the absorbedelémèænts,
=
,
the blood and the
—
“
,'
Ï;;“_
,
ÏŸ
The circulationfof the b'lô0d'in: shès
33) {allows
_
'127
Ganoids and Dipnoi have both and many Teleosts have
neither.
The fact is, that weknoWtoo little about the origin
of these organs.
It. is said, for‘
that'the liver and
pancreas are outgrowths from
mesenterÇn (primitive
gut) and that the liver is the homologue—”of the simple’isac'
.
found in AmphioXus. So far—as the Teleosts are concerned,
one may doubt this derivation ; in such a5case thére
It “seems more 5.probable,—j
that the liver and pancreas arise
the hypoblasttcells'
of the embryo which are actively engaged inconvertirig the
yolk—food before' the 'gut is formed. ' The pyloric cæca,
"
on the other hand, do not develop till much later,
it is
possible that they arise in the samemanner as that suggested
forthe air—bladder, from—the ‘ac(:umulation of Small
'
globules
of air or gases at the Spot where the digestive tract alters
.
—its straight course and makes a _bend ; latér,the duodenum
is formed at this
The pyloric cæca may be correlated'
—
with the pancreas, as some have thought, in so far as their
,
growth iterfereâ with the growth of" the latter and, perhaps
'
,
leads toits di8pe'rSal. ._
'
,'
,
,
'
,
fîîz;yïÎCiRéULÇA“TIoN' A'Nb RESPIRATION,
,
'
'
‘5ï*
aCtiVities ”off digestion 1 and
Within
the organism Would be of _litt—leavail_
present to convey the products from "one place to another.
Onthe one hand, the alimentary Canal is like a retort in which
the most intricate chemical processes we know of, are
constantly reducing the food to a brew suitable for transport
,
through the membranes. On the other hand, the living
tissues are something more than a sieve permitting the
of ”the diss‘olved constituents ;
active cells are
present'selecting the different elements and conVeying them
bloodor lymph (leucocytes), Whilst others arè,busy
removing the ‘ harmful ingredients
,
are two Channels f0r the circulation of the absorbedelémèænts,
=
,
the blood and the
—
“
,'
Ï;;“_
,
ÏŸ
The circulationfof the b'lô0d'in: shès
33) {allows
_