[DG]It would appear, from certain passages of his "Darwinism," that Mr. A. R. Wallace (e.g. p. 139, note) holds or held similar views. "The genera Ateles and Colobus," he says, "are two of the most purely arboreal types of monkeys, and it is not difficult to conceive that the constant use of the elongated fingers for climbing from tree to tree, and catching on to branches while making great leaps, might require all the nervous energy and muscular growth to be directed to the fingers, the small thumb remaining useless." I should also have quoted Mr. Wallace's account of the twisting round of the eyes of flat-fishes—where he says that the constant repetition of the effort of twisting the eye towards the upper side of the head, when the bony structure is still soft and flexible, causes the eye gradually to move round the head till it comes to the upper side—had he not subsequently disclaimed this explanation (see Nature, vol. xl. p. 619). It is possible that Mr. Wallace, notwithstanding the words "constant use" in the passage I have quoted, merely intends to imply that the elongated fingers are of advantage in climbing, and are thus subject to natural selection, the thumb diminishing through economy of growth.
[DH]I find, on rereading one of his articles, that I have here unwittingly adopted one of Mr. Romance's arguments (see Nature, vol. xxxvi. p. 406). The instance Mr. Romanes cites is the curious habit of dogs turning round before they lie down.
[DI]Mr. Darwin, while contending that the modifications need not all have been simultaneous, says, "Although natural selection would thus tend to give the male elk its present structure, yet it is probable that the inherited effects of use, and of the mutual action of part on part, have been equally or more important" ("Animals and Plants under Domestication," vol. ii. p. 328).
[DJ]Midland Naturalist, November, 1889.
[DK]See ante, p. 52.
[DL]Nature, vol. xli. p. 511.
[DM]"Animals and Plants under Domestication," vol. ii. p. 291.
[DN]In the third chapter we saw that in such cases not only are there an enormous number of ova produced, but that (e.g. in aurelia and the liver-fluke) each ovum produces, through the intervention of asexual multiplication, many individuals.
[DO]Cope, "Origin of the Fittest," pp. 226, 125, and 297.
[DP]"Animals and Plants under Domestication," vol. ii. p. 313.