MANNER OP DEVELOPMENT. 57 



But what are we to say about the rudimentary and variable 

 vertebrae of the terminal portion of the tail, forming the os 

 coccyx? A notion which has often been, and will no doubt again 

 be ridiculed, namely, that friction has had something to do with 

 the disappearance of the external portion of the tail, is not so 

 ridiculous as it at first appears. Dr. Anderson"' states that the 

 extremely short tail of Macacus brunneus is formed of eleven ver- 

 tebrae, including the Imbedded basal ones. The extremity is ten- 

 donous and contains no vertebrae; this is succeeded by five rudi- 

 mentary ones, so minute that together they are only one line and 

 a half in length, and these are permanently bent to one side in the 

 shape of a hook. The free part of the tail, only a little above an 

 inch in length, includes only four more small vertebrae. This 

 short tail is carried erect; but about a quarter of its total length is 

 doubled on to itself to the left; and this terminal part, which in- 

 cludes the hook-lilie portion, serves "to fill up the interspace be- 

 "tween the upper divergent portion of the callosities;" so that the 

 animal sits on it, and thus renders it rough and callous. Dr. An- 

 derson thus sums up his observations: "These facts seem to me 

 "to have only one explanation; this tail, from its short size, is in 

 "the monkey's way when it sits down, and frequently becomes 

 "placed under the animal while it is in this attitude; and from the 

 "circumstance that it does not extend beyond the extremity of the 

 "ischial tuberosities it seems as if the tail originally had been bent 

 "round, by the will of the animal, into the interspace between the 

 "callosities, to escape being pressed betv/een them and the ground, 

 "and that in time the curvature became permanent, fitting in of 

 "Itself when the organ happens to be sat upon." Under these cir- 

 cumstances it is not surprising that the surface of the tall should 

 have been roughened and rendered callous; and Dr. Murie,"^ who 

 carefully observed this species in the Zoological Gardens, as well 

 as three other closely allied forms with slightly longer tails, says 

 that when the animal sits down, the tail "is necessarily thrust to 

 "one side of the buttocks; and whether long or short its root is 

 "consequently liable to be rubbed or chafed." As we now have 

 evidence that mutilations occasionally produce an inherited ef- 

 fect,"* it is not very improbable that in short-tailed monkeys, the 

 projecting part of the tail, being functionally useless, should after 



»2 'Proc. Zoolog. Soc.,' 1872, p. 210. 



«3 'Proc. Zoolog-. Soo.,' 1S72, p. 786. 



»* I allude to Dr. Brown-Sequard's observations on the transmitted ef- 

 fect of an operation causing epilepsy in guinea-pigs, and likewise more 

 recently on the analogous effects of cutting the sympathetic nerve in 

 the neck. I shall hereafter have occasion to refer to Mr. Salvin's inter- 

 esting case of the apparently Inherited effects of mot-mots biting off the 

 barbs of their own tail-feathers. See also on the general subject 'Vari- 

 ation of Animals and Plants under Domestication,' vol. ii. pp. 22-24. 



