[62] Animal Life, International Scientific Series, vol. xxxi.
[63] The experiments of Galton and Weismann upon this subject are nugatory, as will be shown later on. But since the above was written an important research has been published by Mr. Cunningham, of the Marine Biological Association. For a full account I must refer the reader to his forthcoming paper in the Philosophical Transactions. The following is his own statement of the principal results:—
"A case which I have myself recently investigated experimentally seems to me to support very strongly the theory of the inheritance of acquired characters, I have shown that in normal flat-fishes, if the lower side be artificially exposed to light for a long time, pigmentation is developed on that side; but when the exposure is commenced while the specimens are still in process of metamorphosis, when pigment-cells are still present on the lower side, the action of light does not prevent the disappearance of these pigment-cells. They disappear as in individuals living under normal conditions, but after prolonged exposure pigment-cells reappear. The first fact proves that the disappearance of the pigment-cells from the lower side in the metamorphosis is an hereditary character, and not a change produced in each individual by the withdrawal of the lower side from the action of light. On the other hand, the experiments show that the absence of pigment-cells from the lower side throughout life is due to the fact that light does not act upon that side, for, when it is allowed to act, pigment-cells appear. It seems to me the only reasonable conclusion from these facts is, that the disappearance of pigment-cells was originally due to the absence of light, and that this change has now become hereditary. The pigment-cells produced by the action of light on the lower side are in all respects similar to those normally present on the upper side of the fish. If the disappearance of the pigment-cells were due entirely to a variation of the germ-plasm, no external influence could cause them to reappear, and, on the other hand, if there were no hereditary tendency, the colouration of the lower side of the flat-fish when exposed would be rapid and complete."—Natural Science, Oct. 1893.
[64] For Professor Weismann's statement of and discussion of these results see Essays, vol. i. p. 313.
[65] Oesterreichische medicinische Jahrbücher, 1875, 179.
[66] Loc. cit.
[67] Essays, vol. i. p. 315.
[68] Les fonctions du Cerveau, p. 102.
[69] Essays, vol. i. p. 82.
[70] As Weismann gives an excellent abstract of all the alleged facts up to date (Essays, vol. i. pp. 319-324), it is needless for me to supply another, further than that which I have already made from Brown-Séquard.