(558' 



MH. J. Li;\V18 lioXIIOTK ON Till 



[Apr. 19, 



curve (dotted line) shows tliree apices :it 2i), 'S'A, and ."55 iinii., 

 and that the female curve shows an apex at 30 and 'Mi with a 

 break in continuity between 32 and 34 ; that is to say, both sexes 

 show tiuee apiees, and that therefore a. larger number of rats 

 ]ia\ e liind feet of those three measurements than of the inter- 

 vening sizes. Now, as these measurements include rats of all 

 ages, and as there is no reason why thei-e should be more of one 

 particular age than another, seeing that the breeding season is 

 fairly continuous throughout the yeai', it follows that we have 

 here three ' limits of gix)wth,' or, in other words, that certain 

 individuals reach their limit of siy.e at these three points, and 

 coiise(|Uently that the numbers at these points tend to accumulate 

 and tlius to form the apices in the curve. Those who accept 

 iMendel's theory would hero m«iutain, and probably with justice, 

 that each apex represents a mutation, and that around these 

 mutations fluctuating variations would occur so that, unless closely 

 examined, the whole series would appear as a case of continuous 

 variation. 



Text-tig. 59. 



Length of Hindfoof in mm. 

 26 27 28 29 3031 32 33 34 35 36 37 38 39 4041 42 



20 



«i 15 







10 



lAuii'. jr. 



<'iiivc lit liiiul-lfiiit iiif'fiMiiTniciil!- ui .Max rnliun lcr(ort(iii ' (ii\\\\is i. \- ii. 



