336 THE EVOLUTION TIIEOKY 



Nc'A'i'rtlu'loHH we know tlmt Man, as n'{;'iu-(lM ccrlaiii I'aJrly luuiioroiis 

 piuiH, is continually and jicrsistcntly \'aryinf;' in a dcHnito diroi'tion. 

 Wiodorshoini, in his bonk On l/ie Kl nu'turc of Ma ii'. cnnincrati's ai lonjj 

 scries of parts and organs ol' tlic luinian liody, which arc in process 

 oi" gradual degeneration, and ol' which it may be jircdicted thai (hey 

 will disappear I'roni tlii^ human structure since they luive lost runctional 

 significance. Among these dwindling sti'nctnrcs are the two last ribs, 

 the eleventh and twell'th, while the thirteentli has ab-ea.dy disa.))pearred, 

 and only occurs t'xceptionally as a, small \'estige in the adult luunan 

 being of to-day. 'riie series includes also the seventh cervical rib, 

 the (W vcid.riile ol' the wrist, the wisdom teeth, and the x-erniil'orm 

 appendix of the intestine. 'V\w. last is nnich larger in nuiny mannrials, 

 and represents an im])ortant ])aii ol' the digestix'c apparatus, but 

 in Man it has dwindled to an nnimiiortant aii]irndag<', which is 

 a source of danger when foreign bodies (cherry stones and sucli like) 

 lodge in it and set up iniiannnation. The variations in its length 

 warrant us in concluding that it is still in process of degt'iuM-ation ; 

 its average length is about 8^ cm., but it varies from a cm. to '23 cm. 

 in length, and in about Sj per cent, of cases a ))art:ial or I'ntire closing 

 up of its opening into the intestine, may be observed. 



Wiodersheim (^numerati^s nearly a luindi'ed parts thus in jirocess 

 ol' degeneration : this means that nearly a hundred structures in Man 

 are at the present time in process of variation, and this couhl not be 

 so unless amphimixis were continually mingling the hereditary con- 

 tributions anew from generaXion to generation, so that the miinis- 

 variations of the ])arts in (piestion, starting from the germ-jilaHm in 

 which they arose at one, time as chance variations, and contiinied in 

 their direction by means of gernn'nal selection, nvv gradually beitig 

 transmitted to all the germ-plasms ol' the s])ecies. We thus see that 

 even in a pei-iod of specic^s-lil'e, which we may fairly ca,ll a ])er'iod of 

 constancy, variations of a phyletic kind are continually in jirocess, 

 whichcouldnot become general without the co-opeiution of amphimixis. 



Now, we have ab-eady s(^en that i)(^rsonal scilection plays no part, 

 01-, at least, no important part in such degenerations, because the 

 variations which ai-e here concerned do not usually attain to selection 

 value, but it is just such variations ])roceiHling with inlinit(! 8lown(^ss 

 that occur in functionally iniportant oi-gans likewise^, and in the pro- 

 gres.sive advance of which personal selection and mutual ada])ta.tion 

 probably play a jiart, so that in this way wi; ca,n understand why the 

 preservation of ainphigony by natural selection must be effected. It 

 is impossible -for obvious reasons — to name ])articular instances with 

 ' (/e6cr rfen Baw (?es Jlfonsc/im, 2nd cd., ProibiM-g-i. -Br., 1893. Trims. London i8g6. 



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