1 66 THE STORY OF THE LIVING MACHINE. 



is equally insistent that there are abundant in- 

 stances of the jnheritance of acquired characters, 

 claiming that these proofs are so strong as to 

 demand their acceptance. Hence this class of 

 biologists insist that the explanation of heredity 

 given as a simple handing down from generation 

 to generation of a germ plasm is not complete, 

 and that while it is doubtless the foundation of 

 heredity, it must be modified in some way so as 

 to admit of the inheritance of acquired characters. 

 There is no question that has excited such a 

 wide interest in the biological world during the 

 last fifteen years as this one of the inheritance of 

 acquired characters. Until about 1884 the ques- 

 tion was not seriously raised. Heredity was 

 known to be a fact, and it was believed that while 

 congenital characters are more commonly in- 

 herited, acquired characters may also frequently 

 be handed down from generation to generation. 

 The facts which we have noted of the contin- 

 uity of germ plasm have during the last fifteen 

 years led many biologists to deny the possibility 

 of the latter. The debate which arose has con- 

 tinued vigorously, and can not be regarded as 

 settled at the present time. One result of this 

 debate is clear. It has been shown beyond 

 question that while the inheritance of congenital 

 characters is the rule, the inheritance of acquired 

 characters is at all events unusual. At the 

 present time many naturalists would be inclined 

 to think that the balance of evidence indicates 

 that under certain conditions certain kinds of 

 acquired characters may be inherited, although 

 this is still disputed by others. Into this discus- 

 sion we cannot enter here. The reason for refer- 

 ring to it at all is, however, evident. We are 



