The Inheritance of Acquired Characters 27 



ance; whatever may be the material basis of ilie defect- 

 ive eyes, is it regularly passed from tlie body of the 

 mother to the young in utero rather than through the 

 germ cell proper ? The answer to this question was early 

 suggested by the following facts. Later litters from the 

 mothers that had originally been treated never contained 

 any defective indi\dduals. The influence of the anti- 

 lens seems to die out in the blood stream, suggesting 

 that it is only by being incorporated in the gemi plasm 

 that the character can be perjoetuated. A more con- 

 vincing demonstration of this point appeared in the 

 later experiments. Males with defective eyes when 

 mated with females from a normal line j:)r(3duced only 

 nonnal offspring. When, however, these same males 

 were remated with their own daughters from the fore- 

 going cross, a certain number of defective offspring 

 resulted. Evidently the abnormality can be passed on 

 by a male parent; it behaves in inheritance like a Men- 

 delian recessive character. Inasmuch as the male parent 

 exerts upon the progeny no influence beyond what is 

 contained in a single male gamete, and inasmuch as this 

 gamete is practically nothing more than a nucleus, the 

 foregoing amounts to about as clear a demonstration of 

 inheritance of acquired characters as would be possible. 

 The very definite results of this set of ex[)eriments are 

 sufficient to prove that inheritance of acquired char- 

 acters can take place, even in one of the higher animals 

 where germ plasm and body plasm must be as sharply 

 differentiated as anywhere. It is equally true, however, 

 that only very special conditions can produce the result. 



A word might be said 011 the theoretical mechanism involved. 

 GuYER proposes that "there is some degree of constitutional 



