DISUSE. One of the negative. but yet button tart. factors of evolution is disuse. lts signifi can•e was first pointed out by Laniard: in his first law of evolution. wherein be says that the constant lack of use of an organ "imperceptibly weakens it. eauses it to become reduced. pro gressively diminishes its faeulties. and end, in it .1.1i example lie gives c reduction and loss of organs or limbs is that oh snakes. which by change of habit from orig inal 13 running to gliding directly along the ground. lane acquired greater length of body. while their legs. being thus disadvantageous to them. have disappeared by atrophy.
11t also 14 of 10011 in the baleen whales and in birds, and in the ant eater. "whose habit of not inastieatimr it- food has been for a long time established and pre served in its lie calls attention to the small reduced fore legs of the kangaroo, whip') "have remained thin, very small, and weak," and especially to the hale. saying: "Indeed, since length of time (luring which these animal- have lived in the depths of the sea, never using their hind feet in seizing objects. their
disused feet have wholly disappeared, as also their skeleton. and Glen the pelis serving as their attachment." Lamarck taught that the effects of disuse are inherited, a doctriuo maintained by 1)arw in. who remarks: "I think there can be no doubt that use in our domestic• animals strengthens and certain parts, and disuse diminishes thein: ;141(1 that such modifications are adding that in free nature animals have structures which can he explained by the effects of disuse." See I 'SE-INI1ERT VANCE.
Darwin also calls attention to the absence in many male dung-lieeth•s, ineluding the -Ntenclius or 'sacred' beetle of the Egyptians, of the an terior tarsi or feet, and this atrophy he thinks it safe to regard "as due to the t.trm. of long continued The saine nay he said of the reduction and loss of the fore tarsi of butter fli•s of the family Nymplialid.e. I:or cases of the loss of eyesight, of and the optic nerves and lobes in animals living in darkness. see