328 SIGNIFICANCE OF SEXUAL REPRODUCTION [V. 



brain of an epileptic animal can reach the germ-cell except in 

 a state of solution, and therefore no direct increase in the 

 germ-plasm can be referred to such molecules, quite apart 

 from the fact that such addition, even if possible, could not be 

 of any value, because the last stage of the epileptic tendency 

 must be represented in the nerve-cells and nerve-fibres of the 

 diseased brain, while the first stage ought to be represented in 

 the germ-cell. 



It may be safely asserted that according to the theory of epi- 

 genesis the germ-cells cannot be influenced except as regards 

 their nutrition. Nutritive changes may be imagined to occur 

 through the varying trophic influence of the nervous system 

 upon the sexual organs, but the structure of the germ-plasm 

 cannot be altered by mere nutritive changes, or at all events it 

 cannot be altered in that distinct and definite direction which is 

 required by the supposed transmission of acquired epilepsy. 



Thus the transmission of artificially produced epilepsy can 

 neither be explained upon the epigenetic theor}^, nor upon the 

 theory of preformation ; it can only be rendered intelligible if 

 we suppose that the appearance of the disease in the offspring 

 depends upon the introduction and presence of living germs, 

 viz. of microbes. The supposed transmission of this artificially 

 produced disease is the only definite instance which has been 

 hitherto brought forward in support of the transmission of 

 acquired characters. I believe that I have shown that such 

 support is deceptive, not because there is any uncertainty about 

 the fact of the transmission itself, but because it is a transmission 

 which cannot depend upon heredity, and is in all probability 

 due to infection. 



Ever since I began to doubt the transmission of acquired 

 characters, I have been unable to meet with a single instance 

 which could shake my conviction. There were many instances 

 in which hereditary transmission was clearly established, but 

 in none of them was there any reason to suppose that the 

 characters transmitted were really acquired. For example, 

 Fritz Miiller has recently informed me of an instance in which 

 he believes that there can be no doubt of the transmission of 

 acquired characters. His observations are so interesting in 

 several respects that I will quote them here. He says in his 

 letter, 'Among the bastards of two species o^ Abutilon, in which 



