Hormones and Heredity by J. T. Cunningham
page 34 of 228 (14%)
page 34 of 228 (14%)
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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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