Inheritance of Acquired Characters 17 



the body of the father that was responsible for the 

 development of a particular type of nose, so there was a 

 similar something in the child's body that produced a 

 similar result. It is merely a matter of convenience to 

 speak of the inheritance of characters. 



Weismann defined an acquired character as "any 

 somatic modification that does not have its origin in 

 the germ plasm." This definition is not always easy 

 to apply. Examples of acquired characters in the 

 Weismaim sense are mutilations, effects of environment, 

 results of function (as in the use or disuse of certain 

 organs), and many diseases that affect the bodily mech- 

 anism. Weismann gave three reasons for rejecting the 

 beUef in the inheritance of such characters: (i) there is 

 no known mechanism by which somatic characters may 

 be transferred to the germ plasm; (2) the evidence that 

 such a transfer does occur is inconclusive and unsatis- 

 factory; and (3) the theory of the continuity of the 

 germ plasm is sufficient to account for the facts of 

 heredity. This last reason has been discussed, but the 

 other two should be considered. 



When Weismann says that there is no known mech- 

 anism by which somatic characters can be transferred 

 to the germ plasm, to him it is equivalent to saying that 

 it is hard to see how the water that has gone over the 

 dam can return and affect the flow of the water upstream. 

 He assumes, of course, that the germ plasm is isolated 

 from the somatoplasm very early in the development 

 of the fertilized egg into an individual, and that when 

 it is isolated it takes no active part in the history of the 

 body (see fig. i). The somatoplasm is thus merely a 

 carrier of the germ plasm and is unable to affect the 



