Hormones and heredity : a discussion of the evolution of adaptations and the evolution of species / by J.T. Cunningham.

  • Cunningham, J. T. (Joseph Thomas), 1859-1935.
Date:
1921
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Hormones and heredity : a discussion of the evolution of adaptations and the evolution of species / by J.T. Cunningham. Source: Wellcome Collection.

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    26 CLASSIFICATION AND ADAPTATION the body, with spinules on the projecting edges, making the skin rough ; lateral line with a semi¬ circular 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. P. cynoglossus, the Witch or Pole-dab : head and mouth smaller than in the Plaice, eyes rather larger ; scales all alike and uniformly distributed, slightly spinulate on upper side, smooth on the lower ; blister-like cavities beneath the skin of the head on the lower side. With regard to the generic characters, it is difficult to give any reason why the mouth should be at the end of the head instead of behind the apex of the snout as in the genus Solea, but, as we have seen already, the small size of the mouth and the greater development of teeth on the lower side are adapted to the food and mode of feeding. It is impossible to say why one genus of Flat-fishes should have the right side uppermost and others, e.g. Sole and Turbot, the left ; it would almost seem to have been a matter of chance at the commencement of the evolution : reversed specimens occur as variations in most of the species. When we consider the specific differences, we find very definite characters in the structure and dis¬ tribution of the scales, and no evidence has yet been discovered that these differences are related to external conditions. There are, of course, slight differences in habits and habitat, but no constant relation between these and the structural differences of the scales. Plaice and Dab are taken together