170
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BIOLOGY OF FISHES
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Teleosts, whereas in the. Elasmobranchs the nerve bres
from each side get mixed up together in a chiasma. In the
normal Teleosts sometimes the left optio nerve is the upper -
one, sometimes the right. In the Flat—shes the upper
nerve is usually the one belonging to the upper, migrating
eye ; but in some cases (Symphurus and Psettodes) it may be [ ='i_Ê î
either the one or the other, and in abnormal specimens
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