_
REGULATION OF FDRM AND STRUCTURES 99
distance covered, worm—like, sinuous; all
of body
approximately equal and attened' from side to side ; no
denitebalanc'e ; tail'straight or diphyCercal ; gut teaching
to_tail. …Làrvaof Clupeids, Dipnoi.=:_ '
'
-—
'
Second form
movement :. slow,Sihùous in.—front,
tWiSting or- rocking behind; head becoming
bending upwards
dorsal n arising postefiorly ; : balance
indenite ; gut being ”m'0ved forwdaway'from tail; = Early
postlarvae'of Clapeids, Eels, and Stufgeon.=
.
"
'
3. Third form of 'movetnent : very rapid movements; ‘
whole body swingihg and rocking from ”the heavy head ’
backwards ; tail strongly heterocercal ; end=of gut removed
from tail ; ventrals‘ï appearig ; balance indenite, but centre
ofgravity near the head. Sharks;
,
,
‘
4. Moderate movements, wave—like, about a denite
centre in'middle of body ; air—bladder develOping—ç: caudal
'
n becoming homocercal; =ar‘1al n appearing; balance
'
more denite, horizontal. Later postlarvæ of Clupeids.
* Ï
_
'
5;. More— rapid movements ; front part-of body' moving
as one piece from sidetd side,poSterior half swingi.üg, rocking;
'
,
or
caùdal region
developed ;, gut and air—‘».
'
;È;d‘ofi‘sÇal and anal developing at the
samet1me
diphycei‘cal
form
* balance hoñZOn—talbùt
”of
Eels, Blé—nies,
Ï‘
_.
'
TheSe Will suice to indicäte‘h9W the various forms may
have arisen and how they developÏ; Many kinds of inter—‘
mediate forms of movement can be distinguished and slow
.
forms appear at
stage.
The body then becomes less
—
compact,
even shapeless, as in the early Ganoids,’
Plectognaths, Pediculates, and Ribbon—shes. Or it may -
’
beCoine‘lbng and‘Eel—like, oreven:wormdike
,
as in theDipnoi
and some of the
Or the rate of movement may”_
'
be.speeded :ùp i-‘to
degree With
regiondeve10ped “into £a remarkab‘le propelling
the Mackerels“and Tunnies.
.
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