226 THE EVOLUTION THEORY 



Nevertheless we know that Man, as regards certain fairly numerous 

 parts, is continually and persistently varying in a definite direction. 

 Wiedersheim, in his book On the Structure of Man^, enumerates a long 

 series of parts and organs of the human body, which are in process 

 of gradual degeneration, and of wliich it may be predicted that they 

 will disappear from the human structure since they have lost functional 

 significance. Among these dwindling structures are the two last ribs, 

 the eleventh and twelfth, while the thirteenth has already disappeared, 

 and only occurs exceptionally as a small vestige in the adult human 

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

 the OS centrale of the wrist, the wisdom teeth, and the vermiform 

 appendix of the intestine. The last is much larger in many mammals, 

 and represents an important part of tlie digestive ap2:)aratus, but 

 in Man it has dwindled to an unimportant appendage, which is 

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

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

 warrant us in concluding that it is still in process of degeneration ; 

 its average length is about 8| cm., l)ut it varies from 2 cm. to 23 cm. 

 in length, and in about 25 per cent, of cases a partial or entire closing 

 up of its opening into the intestine may be observed. 



Wiedersheim enumerates nearly a liundred parts thus in process 

 of degeneration : this means that nearly a hundred structures in Man 

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

 so unless amphimixis were continually mingling the hereditary con- 

 tributions anew from o-eneration to o-eneration, so that the minus- 

 variations of the parts in question, starting from tlie germ-plasm in 

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

 their direction by means of germinal selection, are gradually being 

 transmitted to all the germ-plasms of the species. We thus see that 

 even in a period of species-life, which we may fairly call a period of 

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

 which could not become general without the co-operation of amphimixis. 



Now, we have already seen that personal selection plays no part, 

 or, at least, no important part in such degenerations, because the 

 variations which are here concerned do not usually attain to selection 

 value, but it is just such variations proceeding with infinite slowness 

 that occur in functionally important organs likewise, and in the pro- 

 gressive advance of which personal selection and mutual adaptation 

 probably play a part, so that in this way we can understand why the 

 preservation of amphigony by natural selection must be effected. It 

 is impossible — for obvious reasons — to name particular instances with 



* Ueber den Bail des Menschen, 2nrl cd., Freiburg-i.-Br., 1893. Trans. London, 1896. 



