The transient larval structures of vertebrae, blood vessels and the digestive tract were carefully examined during growth. Constrictions appear in the notochords of larvae prior to formation of the vertebral column. Larvae develop the dorso-lateral condyles between the first vertebra and the exoccipitals, differentiated neural and hemal spines, pleural ribs and epipleurals. The digestive organs exhibit sequential development but structures are not lost or degenerated with growth. The ventral vein beneath the cardinal aorta fragments and degenerates during the transition of larvae to juveniles, and is replaced by the dorsal vein. The formation of the dorsal vein completes beneath the cardinal aorta in larvae about 7.0 mm TL. This apparent shift of the ventral to the dorsal vein in the tail differs from the subsequent shift in the trunk where the ventral vein does not degenerate. The dorsal vein completes from the trunk to the tail until 14 mm TL.
Growth of the Medaka (I) – Formation of Vertebrae, Changes in Blood Circulation, and Changes in Digestive Organs
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