Drawings of developing larvae of the tailed species (M. oculata), tailless species
(M. occulta), and their hybrids in section showing different tissues. Green: brain and spinal
cord. Red: mesenchyme. Orange: endoderm. White: tail muscle. Red: notochord. Note that the
notochord and tail muscle cells are present but not extended into a tail in the tailless species.
A tail with notochord cells (as well as the brain sensory organ in black) is restored in the hybrid.
A gastrula stage embryo hybridized in situ with a probe specific for the FH1 forkhead gene. The
forkhead gene is expressed in gastrulating cells.
In situ hybridizations showing expression of a muscle actin gene during embryogenesis of the tailed species
(left column), the tailless species (middle column), and their hybrid (tailless X tailed) (right column). The muscle actin gene is not expressed in the tailed species but expression is restored in the hybrids.
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