7006

• UCREFRP Catalog Number: 7006
• Author: Gustafson, E.
• Title: Early Development, Adult Sexual Dimorphism, and Fecundity of the Razorback Sucker,
• USFW Year: 1975
• Copyright Material: NO

'll.e brain cavities awl sJ;lual cO.ru nave formed by contraction
of the neural plate. ine eye rudlffi~lts h~ve formed and are seen as
I
lat~ral fJI'otrusio!ls a.t the C:i.l~';,0riGr ellG. o~' tnt; ol'ail!. 'I'he prosen-
cephalon (fore0rai~), mesencephalon (midbraiu) ~ld rhombeficaphalon
lhia~~rain) are easily distll~uisheJ. T~e auditory vessicles arc
forillll~ at the level uf the hindbrain. 1he first pair of somites
have formed.
Stage 18: Cavities in the Eye Rudiments: 53 hr.
'The optic placodes (eye rUG iments) have elongated and contain
narrow vessicles. ihe head fold is now visible: subcephalic pocket
and ant-erior intes'cinal portal are ventrad. to heau. 'lhe auditory
placodes are formed. There are now 14 to 16 pairs of samites.
St.age 19.: Ovalt.;,y8s: Yl hI'; 2.5 laIn. U'ig. 2g).
- ~hc optic.placodes are rounded to oval. Vessicles are not yet
pI'esen~ in the ~uditQry placodes. There are thirty pairs of somites.
'ih<:: t.ail process is quite dist.inguished.
stage 20: Early'l'ailbud: 65 hI'; 3.0 Iillil. (Fig. Ja).
The optic vessicles are somewhat flattened on their outer mar-
gins: The leas i3 nu~ forming. 1~e audi~ory ~lacodes have develop-

8-.'~ .:..:.. ~11.~11

,-. ," : -.: ,
_:..-.,. 'J ..i. ...,.; .

.:i. :::::::..:...:'1 l.al._t.-u.l ~;:c-:.:; G.0velopej and protrudes from

tfle yolk. sphere. '1:1e foregut is forming.
Stage 21: Late 'l'ailbud.: da.y 4; 78 hI'; J.8 mm. (F'ig. 3b).
'1'he embryo is subdivided into two parts: anterior portion con-
sisting of head and anterior tru.llk overlying spherical yolk mass;
posterior portion consisting of posterior trunk and tail overlying
cylind.ri cal ~'olk mass. 'Eba opt i c st8.1 k s and cups can be di stingui sh-
ed as well as the lens. 'rhe prose~"lc;.Jp;l-::llon is .colOW divisible into
telencephalon (future cerebrum) and diencephalon (future epithalamus,
t.nalalilus and hypothala::a.us); the rhombeflcephalon is now divisible in-
(,0 Ii1e l.encephalon. (fu "LUl'!.:: cere bellum) . and illyeleLlcephalon (future med-..
ulla oblongata). ..I.he heart rudiment 1.:3 preseLlt. 'Ihe tailbud is '

1 eL16 t hellinE,.

'l'he enbl''yo is motile witilill the egg chori.oLi.

SLube 22: Heart. Beat: c.J h1'; 1':'.0 lili!l.

"

-~;-, ,....~ -~- ~:'I'_:':" '

, ~'" ~~.\,,----:-,-,...; -9":"'''-,

.a_........_.....~ ..._.._..,....- ....._.....~...__ . ..,..,-_