THE LIVING MACHINE BUILDING FACTORS. 165 



the germ plasm within the reproductive glands 

 is not, so far as we can see, subject to the influ- 

 ence of an increased use, for example, in the arm 

 muscles. The germ material is derived from the 

 parents, and, if it is simply stored in the individ- 

 ual, how could an acquired variation affect it ? If 

 an individual lose a limb his offspring will not be 

 without a corresponding limb, for the hereditary 

 material is in the reproductive organs, and it is 

 impossible to believe that the loss of the limb can 

 remove from the hereditary material in the repro- 

 ductive glands just that part of the germ plasm 

 which was designed for the production of the 

 limb. So, too, if the germ plasm is simply stored 

 in the individual, it is impossible to conceive any- 

 way that it can be affected by the conditions 

 around the individual in such a way as to explain 

 the inheritance of acquired variations. If ac- 

 quired variations do not affect the germ plasm 

 they cannot be inherited, and if the germ plasm 

 is only a bit of protoplasmic substance handed 

 down from generation to generation, we can not 

 believe that acquired variations can influence it. 



From such considerations as these have arisen 

 two quite different views among biologists ; and, 

 while it is not our purpose to deal with disputed 

 points, these views are so essential to our subject 

 that they must be briefly referred to. One class 

 of biologists adhere closely to the view already 

 outlined, and insist for this reason that acquired 

 variations can not under any conditions be in- 

 herited. They insist that all inherited variations 

 are congenital, and due therefore to direct varia- 

 tions in the germ plasm, and that all instances of 

 seeming inheritance of acquired variations are 

 capable of other explanation. The other school 



