8
' .
'THE* BIOLOGY OF FISHES ,
the latter,
It may be pôintéd upwarcls as in the Star—gazeis
(Uranosc0pus) or downwards as in the Mormyrsof theNile.
Sbmetimes the jaws protrude forward in asnout with a tiny
'
“mouth at the front end as in the Pipe—shes', s0metimes they
are
drawn backwards until the head seems all mouth, as
-
in the 'Angler or Frog-sh (L‘Ophius) and Gastrostomids
(FigS. 4,
10).
'
_
:
,
,
‘
.
,
natural position of the mouth is in front, as it
in
the
shes, but in many the jaws have been pulled
down;ànd backwards and a snOut _has grown out above.
Thus, in the Sharks and Rays the mouth is always venttal
,
and drawn out sideways in a_creScent. As will be Seen later,
'
able to connect this
shape with the mode of
life and movements of the early embryo. These. are
,
cartilaginous-(gristly) shes with an impressionable structure,
but even some-ef the bony shes have the mouth in a ventrà‘l
position,
for example, the Macrurids, allies
"
of the Cod, and the Common Sole. In the Œ'laice (Fig. 3),
the mouth opens sideways, a—. peculiarity shown by some
other at-shes but not by all.
_
—
—
"
—
..
_
Round the mouth there may be fi“inges of skin 'or barbels
5
(b in Cod, Fig. 2), which have a tactile function, that;is to
say, without seeing their
these shes can
“
feel
” for it.
This is specially noticeable in the case of the Cat—shes
(Silùroids), which have a number of sensitive barbels round
the jawS, and can be seen to make use… of them when living
in aquaria. ï>;The RedMulletfhas
thé-{ _"thr‘0at, j_, Whilst other
the
ï
Gurnards, usethe1rnsfor thatpurpose
?
_
[
commen:
no”StrilS
,
lie
the : ’snout,
each with two openingsas "a rule, but Sometimes onlÿone.
In * the Sharks
the nostrils are the*deep
openings onthe ventral surface justin front of
mouth;
:,
There is no
in these, but in the Lung-shes
(Dipno‘i) the n'ose cémmunicates‘with the mouth.
,
‘
,
'
:;
Shesare uSually, very large,
larger than in the Sharks, Rays, and Lung—shes,—and this
:
—ÏCàn.’alsO-be Connected With the mode of life of
_