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ARE ACQUIRED CHARACTERS HEREDITARY? 335 



Neo-Lamarckism. — Many modifications of the Lamarckian 

 hypothesis of the inheritance of acquired characters have been pro- 

 posed in recent years. Foremost among those are the "mneme" 

 theory of Semon and the "centro-epigenesis" theory of Rignano. To 

 Semon as to many other biologists the apparent resemblance between 

 memory and heredity has seemed significant, and this furnishes the 

 basis of his theory. Semon holds that every condition of life, every 

 functional activity of an organism leaves a permanent record of itself 

 in what he calls an "engramme." If these conditions or activities 

 are long continued their engrammes are heaped up and affect heredity. 

 Semon does not ask if "acquired characters" are inherited, but rather 

 "Are the hereditary potencies of the germ cells altered by stimuli 

 acting on the parental body?" This is a very different thing from 

 the inheritance of a particular acquired character, and there is some 

 evidence that such stimuli may in rare instances produce changes in 

 the hereditary constitution of the germ plasm though these evidences 

 are by no means conclusive. 



Temporary effects of environment; "induction." — On the other 

 hand certain changes may be produced in germ cells or embryos which 

 last for only a generation or two and then disappear. It is well known 

 that plants grown in poor soil are smaller and produce smaller seeds 

 than those grown in good soil, and De Vries, Bauer and Harris find 

 that such seeds produce smaller plants having smaller seeds than do 

 seed of normal size. This is an after effect of poor nutrition which 

 changes the amount of food material in the seeds and through this the 

 size of the plant which develops from the seed, but it does not change 

 the hereditary constitution. Woltereck found that in Daphnia there 

 is an after effect of cold lasting for one or two generations, and this he 

 calls "induction," when the effect lasts for one generation, or "pre- 

 induction " when it lasts for two or three generations. Whitney found 

 that rotifers poisoned with alcohol were weaker in resistance to copper 

 salts and were less fertile than others, and when brought back to 

 normal conditions the first generation was weak but the second was 

 normal. On the other hand Stockard finds that the injurious effects 

 of alcohol on guinea pigs persist through two or more generations. In 

 man alcohol may have an "induction" effect on offspring, but fortu- 

 nately it does not seem to alter hereditary constitution. Probably of a 

 similar character are Sumner's results; he found that mice raised in the 

 cold have shorter tails than those raised in higher temperatures and this 

 modified character appears in the next generation. If this is an after 

 effect or "induction" it should disappear in the following generations. 



