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Hormones and Heredity by J. T. Cunningham
page 34 of 228 (14%)
constitutional asymmetry of head or body, but a modification of different
organs independently of each other in relation to external conditions--
light, food, movement.

On the other hand, let us consider some of the diagnostic characters by
which species and genera are distinguished in the Flat-fishes or
Pleuronectidae. The genus _Pleuronectes_ is distinguished by the following
characters: eyes on the right side, mouth terminal and rather small, teeth
most developed on the blind (left) side. Of this genus there are five
British species, namely:--

_P. platessa_, the Plaice: scales small, mostly without spinules, reduced
and not imbricated, imbedded in the skin; bony knobs on the head behind
the eyes, red spots on the upper side.

_P. flesus_, the Flounder: no ordinary scales; rough tuberoles along the
bases of the marginal fins and along the lateral line; these are modified
and enlarged scales; elsewhere scales of any kind are absent.

In these two species the lateral line is nearly straight, having only a
slignt curve above the pectoral fin.

_P. limanda_, the Dab: scales uniform all over the body, with spinules on
the projecting edges, making the skin rough; lateral line with a
semicircular curve above the pectoral fin.

_P. microcephalus,_ the Lemon-dab: scales small, smooth, and imbedded;
skin slimy, head and mouth very small, colour yellowish brown with large
round darker marks.

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