VARIATION AND HEREDITY 121 



clearly, especially from the pioneering work 

 of Gallon, that th^-iLJ3iten^^ 



particular varia- 



' 



imrl tliA gr^nn^ of it,,^ rleyinti'rm frnryi 



the mean of the character in question. Let 

 us take Wallace's illustration, which makes 

 this point clear at a glance : Among measure- 

 ments of 2,600 men, taken at random, there 

 is 1 of 4 ft. 8 in. and 1 of 6 ft. 8 in.; 12 of 5 ft. 

 and about 12 of 6 ft. 4 in.; i.e. equal num- 

 bers at equal distances from the mean of 5 ft. 

 8 in. In^ other words, when the frequency 

 aiid the magnitude of the _yariations are 

 registered^ they often show 

 Normal 



This tedious task of registering the varia- 

 tions that occur may seem far from life-lore, 

 but a little con.sidqrq.tion and a little actual 

 ypgiqfrQ-Mm^ ftf Buttercup petals^ of length 

 ofjnrd wjngs. of hrit,t,)e-star arms, of jelly-fish 

 qanals. or th^ Hke^ will onuviTipp f|ie ^student 

 that hioTnet.rics may lead him into the very 

 hefl.rt. of thfi matter. If the registration of 

 the dimensions of a particular character be 

 carried on year after year in similar material, 

 and show a consistent increase in the asym- 

 metry or skewness of thq curve, this rmist 

 meanjjiat the species is moving JT] ^. definite 

 direction as regards the particular character 

 measured. Similarly, the persistent occur- 



