28o Habit and Instinct. 



CHAPTEE XIII. 



AEB ACQUIRED HABITS INHERITED ? 



Attention has already, more than once, been drawn to 

 the distinction between variations on the one hand and 

 modifications on the other. Variations take their origin 

 in the germinal substance from which the organism is 

 developed, and are unquestionably hereditary. Modifi- 

 cations are acquired in the course of individual life, being 

 impressed, not primarily, if at all, on the germinal sub- 

 stance, but on the bodily tissues which are developed from 

 the germ. And whether they are hereditary or not is the 

 question we have now to discuss in its relation to habit and 

 instinct. If they are hereditary, their effects must be in 

 some way transferred from the bodily tissues to the 

 germinal substance, so as to become a source of variation ; 

 modification in a given manner in one generation giving 

 rise to a variation of similar nature in the next generation. 

 Take a particular case. No one is likely to question 

 the fact that the maternal instinct of hens is subject to 

 variation. Some are good mothers, some bad; and it is 

 customary to select the good mothers to rear stock, a 

 procedure based on the belief — founded on practical ex- 

 perience — that such excellence is hereditary. It would be 

 interesting — if not very profitable — to experiment in the 

 opposite direction ; to set the bad mothers' eggs under good 



