here by hypothesis an elongated neck; it is conceivable that out of large herds the few survivors of a drought might be exclusively such as possessed this advantage to some extent. These would probably transmit to a large majority of their descendants the tendency to vary in a given direction which they had themselves all more or less exhibited. Their progeny, moreover, would be placed in exceptionally favourable circumstances by the very fact that in the previous drought so many of the same species had been starved to death, who would otherwise have furnished their chief competitors in the struggle for existence. It is still objected that upon this supposition many other animals ought to have acquired giraffe-like necks. But such an expectation is far from being warranted by the principles of Natural Selection. Since all variations are potentially useful, but only those are preserved which suit the surrounding conditions among which they are exhibited, the calculation of chances will itself plead for the probability that a variety of variations will be preserved, rather than the same many times over. Other species competing with the giraffe for food would be little likely to gain an advantage over it by a slight increase in length of neck, though by other variations they might achieve a decided superiority. It is obvious, also, that the advantage assigned to the elongated neck would belong to many other possible variations, such as a lengthened proboscis, far-reaching arms, the climbing powers of the snake or the monkey, the flight of the bird or the insect; all of which may be due to Natural Selection and the subsidiary principles which the theory of Development embraces. The calling in of subsidiary principles may be thought to spoil the boasted simplicity of the theory. But such an opinion is hypercritical. One might truthfully say of a great patriot that all he did was in obedience to the simple law of duty, without implying that he was exempt from the law of association of ideas, or independent of the mechanical, chemical, and vital laws which regulate many of the functions of all human beings alike. FOOTNOTES. [1] These papers were read at various dates between February 1869 and January 1871, before the Torquay Natural History Society. [2] Read before the Devonshire Association, July 1870. [3] Horace, Odes, I. xvi. 13:-- Fertur Prometheus addere principi Limo coactus particulam undique Desectam, et insani leonis Vim stomacho apposuisse nostro. [4] Lyell, ‘Principles of Geology,’ vol. ii. p. 324. Tenth Edition. [5] Darwin, ‘Animals and Plants under Domestication,’ vol. ii. p. 251. [6] 1,073,741,824 grains. [7] ‘On the Origin of Species,’ p. 74. Fourth Edition. [8] Darwin, ‘Animals and Plants under Domestication,’ vol. ii. p. 379. [9] 37 dwts. 7 grs., or 895 grs., between seven and eight times the size of the wild fruit. See ‘Animals and Plants under Domestication,’ vol. i. p. 356.