CHAP. XX 



Heredity 331 



exactly through, the body ; but this is a distinction loj 

 subtle to be verified. 



These two saving- clauses seem to me to aflfect the strin- 

 gency of Weismann's conclusion, but in his view they do 

 not affect the main proposition that definite somatic modifi- 

 cations or changes in the body due to function or environ- 

 ment have no effect on the reproductive cells, and therefore 

 no transmission to offspring. 



{c) Arguments against Weismann's position. — In arguing 

 against Weismann's position that no acquired characters 

 are inherited, I shall first illustrate the arguments of others, 

 and then emphasise that which appears to me at present 

 most cogent. 



(i) Some have cited against Weismann various cases 

 where the effects of mutilation seemed to be transmitted, 

 and Weismann has spent some time in experimenting with 

 mice in order to see whether cutting off the tails for several 

 generations did not eventually make the tails shorter. It 

 did not — a result which might have been foretold. For we 

 have known for many years that the mutilations inflicted 

 on sheep and other domesticated animals had no measur- 

 able effect on the offspring. Even the numerous cases of 

 tailless kittens produced from artificially curtailed cats have 

 no cogency in face of the fact that tailless sports often arise 

 from normal parents. Moreover, it is for many reasons not 

 to be expected that the results of curtailment and the like 

 should be inherited. For there is great power of regener- 

 ating lost parts even in the individual lifetime ; the result 

 of cutting off a tail is for most part merely a minus quantity 

 to the organism ; the imperfectly known physiological re- 

 action on nerves and blood-vessels might perhaps result in 

 a longer rather than a shorter tail in the offspring. 



(2) Various pathologists, led by Virchow, have empha- 

 sised the fact that many diseases are inherited, but their 

 arguments have usually shown how easy it is to misunder- 

 stand Weismann's position. No doubt many malformations 

 and diseases reappear through successive generations, but 

 there is lack of evidence to show that the pathological 

 variations were not germinal to begin with. It is sadly 



