590 EXPERIMENTAL FISH EMBRYOLOGY 



NORMAL DEVELOPMENT OF FUNDULUS HETEROCLITUS AT 25"C. 



Developmental atase 



Unfertilized egg. 



1 cell. 



2 cell. 

 k cell. 

 8 cell. 

 l6 cell. 

 52 cell. 

 61+ cell. 

 128 cell. 

 256 cell. 



Early high bias tula 



Late high blaatula 



Flat blaatula 



Expanding blaatula. . Blaatula enlarges. 



Gaatrulation begins. Early gaatrula. 



Blastoderm about one- third over surface of yolk. 



Blastoderm about one-half over surface of yolk. Middle gaatrula. 



Blastoderm about two-thirds over surface of yolk. 



Blastoderm about three-fourths over surface of yolk. 



Embryonic shield condenaes to form keel. 



Optic vesicle first visible as an expansion of the forebrain. 



Large yolk plug. 

 Small yolk plug. 

 Blaatopore cloaes. 

 First somites formed. 

 Four somites. 

 Optocoele develops. 



Auditory placode forma. Optocoele connects across brain. 

 Optic cup forms, and lens develops. Neurocoele develops. 



About 10 somites. 

 Expansion of the mid-brain to form the optic lobes. 

 Melanophorea first appear on yolk. 

 Melanophorea appear on embryo. 



Heart pulsates. No circulation. Hind- brain enlarges. 

 Circulation begins, through dorsal aorta and vitelline veaaels. 

 Circulation through ducts of Cuvier. 

 Otolitha develop. 

 35 somitea developed. 

 Pectoral fin bud appears. 

 Retinal pigmentation begina. Urinary vesicle formed. Caudal 



fin begins to develop. 

 Liver develops. Cartilage begins to differentiate. 

 Pectoral fin round. 



Lens of eye Just obscured by retinal pigmentation. 

 Pigmentation of peritoneal wall. 

 Circulation in pectoral fin. 

 Fin rays in caudal fin visible. 

 Air bladder develops. 



Neural and hemal arches in vertebrae in tail are developed. 

 Head flexure begins to straighten out. 

 Head flexure nearly straightened out. 

 Mouth opens. 

 Hatching. 

 Pigmentation of air bladder. 



(FromSolberg I958: Jour. Exp. Zool. iQ-.kk'y) 



