240 DEVELOPMENT AND HEREDITY. 



but on the contrary, the facts of embryology and 

 morphology point to a negative conclusion. The 

 epidermis cells from which the brain develops seem 

 to be like all the other epidermis cells, and among 

 worms and other lower animals parts of the nervous 

 system when cut out may be replaced by a new 

 growth from other cells around them. Since, there- 

 fore, the brain cells possess the power of purposeful 

 response to stimuli, can the purposeful response 

 of the other cells, sprung from the same blastoderm, 

 be attributed to a totally different property .' 



An instinct or habit of action is not essentially 

 different from a habit of growth. We have seen 

 how the habits of growth and development were 

 formed by long continued repetition of mechanical 

 reactions, and how they perpetuate themselves in 

 the hereditary impulse. In the same way, the 

 more complex reactions of an animal, such as feed- 

 ing, reproducing, nourishing, and protecting the 

 young, being repeated in each generation, tend by 

 repetition to become as much a part of the heredi- 

 tary impulse as the growth or development itself. 



It is interesting to note the fact, that when any 

 action is repeated a great number of times, although 

 at first it is only with great difficulty that the action 

 can be performed twice exactly alike, yet finally, 

 after a great many repetitions, the successive per- 



