footnotes
[1] HOPKINS, W.: Cambridge Philosophical Transactions, Vol . VI, pp. 43-45.

[2] DARWIN, CH.: Transactions of the Geol.Society of London, 2. Ser.Vol. V. 1840, p. 626.

[3] Ibid.

[4] DARWIN, op. cit., p. 629.

[5] DARWIN, op. cit., p. 619.

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