Teleosj‘ts,
thenumber is
under‘the
,
coms—med;inuencesëchf the
and "the”
.
Ï _
‘
__cohditi0hs._
"
'
»
'
=As theïsh grows and the
develop,
the
the nerve cord come topress upon
_
the” sides ofthe small
cemented thereto,
as it were, by:.cartilaige. WVith the continued pres‘sure of
:
-
these
the 'cylinders take on the
Ëshapeof anhour—glass,most typièally seen in the Clupeids.‘
OneXamimngthe
of a Herring We nd that they
remain
lled With the
substance
'
_
and »‘W‘ithout ossiëËd bounding»'merbranes.
'
f
_“ Th1s is the simplest form of
in the shes,
7
and may be added
characters of the
'—
Clupeids. Further progresser differentiation c‘onsists' in
cartilage of ”the arches ’Worikihg its way —roùnd the
Cylinders and rèplacing
t11e'original bony
covering. Then—“the Cartilage 1tS€lf
and
we get the more diversied=vertelâWe see;
theÇod orPerch,w1th theboundmgmembrane also Oss‘iÈèdg_
=
andshowmg annual rings;
'
'
Palæozoic period the
deposited more in the skin than
9
,_
in the vertebral
more especially in—_ the head
at least
most of the forms preserved as fossilS.
These “appear to have been-sloW-ïoVin‘g— _sh—eSÏ 11v1ngonthe
…… ndnfh Water— Thpbb1tythth
;
athéir excretary systemwæ —
;
; *
1nferwrtowhatwendmtheèheäiof'k Epresent day
_]
;
'
:_
modern shes, and1t1s
_
therefore—not easÿ‘tosayê Whether =shes
_Ï
-