36 INHERITANCE IN SILKWORMS, I 



perhaps, indeed, within the same strains, the Mendelian behavior is 

 lost, and even the discontinuous or alternative nature of the 

 characteristics breaks down. 



These different conditions displayed by the inheritance of larval 

 and cocoon characters are to my mind extremely suggestive. They 

 seem to me to indicate pretty clearly strong differences between 

 naturally established and artificially established characters; they seem 

 to indicate the difficulty of explaining fixed strain, race and species 

 differences on the basis of selection of fluctuating variations ; they seem 

 to point toward explanation of such differences on the basis of dis- 

 continuous variations or mutations; but they seem, finally, to indicate 

 an essential likeness, at bottom, between characteristics established by 

 the selection of fluctuation variations and characteristics established by 

 the appearance, full-fledged, of potent discontinuous variations. The 

 differences established by the selection of fluctuating variations seem 

 to require a long period of time to get upon that safe ground of inde- 

 pendence which is attained almost at once by the difference established 

 by discontinuous variations or mutations. And yet the fact seems 

 plain that in a long time both kinds of differences will come to rest 

 upon and be possessed of the same inheritance behavior and potency. 



