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<br />556
<br />GREAT BASIN NATURALIST
<br />Vol. 42, No. 4
<br />December M
<br />FF
<br />CdV
<br />Fig. 3. Embryo o
<br />rion not depicted. I
<br />CA = carotid arter
<br />DA = dorsal artery
<br />vein, SV = sinus vei
<br />tory vesicles at level of hindbrain; first pair
<br />of somites present.
<br />Stage 18: cavities in eye rudiments, 53
<br />hours. Optic placodes elongated, containing
<br />narrow vesicles; head-fold visible; sub-
<br />cephalic pocket and anterior intestinal portal
<br />ventral to head. Auditory placodes formed;
<br />14-16 pairs of somites.
<br />Stage 19: oval eyes, 57 hours, 2.5 mm (Fig.
<br />1H). Optic placodes rounded to oval; vesicles
<br />not yet present in auditory placodes; 30 pairs
<br />of somites. Tail process distinguishable.
<br />Stage 20: early tailbud, 65 hours, 3.0 mm
<br />(Fig. 2A). Optic vesicles flattened on outer
<br />margins; lens forming. Auditory placodes
<br />with small vesicles. Tailbud developed; pro-
<br />truding from yolk sphere. Foregut forming.
<br />Stage 21: late tailbud, day 4, 78 hours, 3.8
<br />mm (Fig. 2B). Anterior portion of embryo
<br />(head and anterior trunk) overlying yolk
<br />sphere; posterior portion (posterior trunk and
<br />tail) overlying cylindrical yolk mass. Optic
<br />stalks, cups, and lenses distinguishable. Pros-
<br />encephalon divided into telencephalon (fu-
<br />ture cerebrum) and diencephalon (future
<br />epithalamus, thalamus, and hypothalamus);
<br />rhombencephalon divided into meten-
<br />cephalon (future cerebellum) and myelen-
<br />cephalon (medulla oblongata). Heart rudi-
<br />ment present; tailbud lengthening, embryo
<br />motile within chorion.
<br />Stage 22: heart beat, 83 hours, 4.0 mm.
<br />Heart pulsations noted. Tail at right angle to
<br />body axis. Kidney ducts (pronephric dt -.
<br />and dorsal aorta formed ventral to nc> ;•;;1
<br />tube and notochord; alimentary tract ' -d
<br />by endoderm and nearly complete; str_: .;-
<br />deum and proctodeum not apparent.
<br />Stage 23: fin fold, day 5, 103 hour..
<br />mm. Fin fold appearing on tail and post ` n
<br />dorsum; head growing outward from
<br />sac. Circulatory system formed; nasal.
<br />codes present; tail beginning to straights
<br />Stage 24: blood circulation, 117 hour:.. 8
<br />mm (Fig. 3). Head extending from
<br />Heart visible within pericardial ca
<br />flexed, sinus venosus and atrium lying :, c
<br />and left of ventricle and conus arte, -s;
<br />endocardium and epimyocardium ?-
<br />tinguishable. Three visceral (gill) a !s
<br />formed; pupils visible within eyes, L" 'n
<br />pigment granules in choroid regions. Yo`' e-
<br />duced to cylinder below body axis. : )d
<br />flow: atrium - ventricle - conus arteric, . .
<br />ventral aorta - branchial afferents € r
<br />chial efferents dorsal aorta and in: a]
<br />carotid arteries vitelline artery - ce,: aal
<br />vein - posterior cardinal vein - anterior ;. :r-
<br />dinal and vitelline veins -> common car_; ,al
<br />vein (Duct of Cuvier) -> sinus veno,, - -
<br />atrium. Embryos extremely motile, som, '-e-
<br />ginning to rupture chorion.
<br />Stage 25: pectoral fin rudiments, M
<br />hours, 6.8 mm. Pectoral fin anlagen ai wr-
<br />ing posteriad and ventrad to au.; )rn'
<br />vesicles. Tail slightly upturned. Stoma im
<br />clearly visible. i
<br />yolk. Embryos fl
<br />beats.
<br />Stage 26: pec
<br />hours, 7.3 mm.
<br />protrude, slightl
<br />Head continuing
<br />yolk.
<br />
<br />
<br />
<br />Prolar
<br />Stage 27: hat
<br />(Fig. 4). Pectoral
<br />straightened and
<br />anteriorly on dor:
<br />relative to body a
<br />eye pigment inc
<br />motile, flexing alc
<br />movements.
<br />Stage 28: 142
<br />arches visible; h
<br />angle to body axis
<br />CFf
<br />Pr
<br />VFf
<br />Fig. 4. Prolarva of r
<br />and AT = alimentary
<br />y ity, PFb = pectoral fir
<br />Fig. 2. Early (A) and late (B) tailbud embryological stages of razorback sucker, Xyrauchen texanus; chorion , -
<br />moved-embryo extended in "B." Legend as in Figure 1 when applicable, and AV = auditory vesicle, Di = .
<br />cephalon, FG = foregut, L = lens, Met = metencephalon, Myl = myelencephalon, N = notochord, OC = ::ic
<br />cup, OV = optic vesicle, TB = tailbud, and Te = telencephalon.
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