Heredity and Education. 337 



the formative period of childhood and youth; hence the high 

 value of the expert direction during this time. 



Whenever the same response is continued through many 

 generations the part of the body affected by this use. or disuse 

 becomes permanently modified in heredity. The pineal body 

 in man's brain is believed by most anatomists to be the rudi- 

 ment of a third eye. This unpaired eye is still functional in 

 certain reptiles. Mammals of two million years ago had 

 brains far less well developed in the upper front and rear por- 

 tions than the brains in mammals of the same size of body to- 

 day. It should be noted that the organs of man's body orig- 

 inated so far back in the ancestral line and in such a simple 

 way that they were but slight modifications of preexisting 

 parts. As the developing parts increased in size and efficiency 

 through use their formation came to be more and more an un- 

 conscious function of the ego, and thus became an inheritance. 



5. But ivhat are the proofs of the inheritance of the effects 

 of use and disuse ? 



In considering this question it must be remembered that the 

 rate at which new modifications of parts and at which new ad- 

 ditions or subtractions to powers pass into the domain of 

 heredity is of necessity exceedingly slow. Persistence in use 

 or disuse for many generations is necessary to make much 

 change, consequently the long periods of geologic time must 

 elapse before the modifications are very noticeable. There- 

 fore, the geologist is the only scientist who is fitted to answer 

 this question with assurance, and he says, after examining 

 the fossil remains of thousands of fish, amphibians, reptiles, 

 birds and mammals, that acquired parts are inherited and dis- 

 used parts are slowly lost. 



The brain cavity of mammals, for example, ha^ increased in 

 size several times during the Tertiary and Quaternary peri- 

 ods ; this increase apparently keeping pace with the more and 

 more strenuous struggles for existence, demanding the greater 

 use of wit. Cope discovered that the primitive molar tooth of 

 mammals was tritubercular, with simple, conical tubercles. 

 Osborne says that nearly all kinds of mammals — hoofed quad- 

 rupeds, monkeys, carnivores, insectivores, rodents, marsu- 

 pials — are found building up their grinding teeth on the basis 



22— Sci. Acad.— 2163 



