148
_
THE, BIOLOGY OF FISHES
'
stomach and gut are not altogether
“
involun‘tary
”
under the control of the sh.
On the other hand, although *
the muscles opening and closing the mouth consist mostly
of striated bres, yet in forms with large and powerful
’
'—
mouths the basal part near the skull shows the smooth
kind;
Thus, a stronger and longer contraction of the jaw's- :
is permitted, whilst the rapidity of opening and shutting of
:
the mouth is not interfered with.
This adaptation is seen
,
very well in the Eel.
Similarly, the muscle bres of the
ns are less striated as a rule than those of the body, showing
:
that their movements are to some extent involuntary.
Ï
These dierences are due apparently to “the varying
proportions of the ground—fsubstance (sarcoplasm) and
_,
brillæ and probably represent a difference in the use of the
various muscles, but very little is known as yet regarding _' «33,
the
‘
between“- structure and function of the 52
dierent kinds of muscle cells;
.
-
''
r
‘The colour of the muscle in shes is usually white or
grayish, and this may be connected with the curious;.fact,
i _ ;
that the consumption or oXidation of foodstuffs is very
complete in shes (Pü-tter). Corresponding to this the heat —
.
produced-is “usually small in amount, the temperature within
.
.
the deep—seated muscles being only about %,to
higher
than that of the surrounding water (Simpson, 1908). ; The;
lVI‘ackerel family, especially the
The temperature j:of
'
may be=10° C. higher than
ofthemusclers offa
“Or red ‘
É
least in dead
:
shes,andthedarkœt par—ti. of£=the muscles in the Tunnies
Ï
_.»
supplied
(Kishinouye, 1923).
,
_
InthéPikè_zdDOg—sh,Acanthias, Ki‘dder found a temperature
of
the surrounding water and even more
.Ï_
than this in the embryo. .
_
.
_Ïf
-
The brown colour maybe due in part.to the infuSi0n of
_.
:»
blood into the tissues,
but in any case it is a sign of greater
Ê
T
metabolism, and“it’
signicant that the ‘ElasmŒ
branchS, grid even the embryos, should display
—