TEANSMISSIBILITY OF FUNCTIONAL MODIFICATIONS 99 



cannot even be considered as the transmission of a particular morpho- 

 logical lesion. 



We may regard as indirect proofs such facts as can only be 

 explained on the assumption of this mode of inheritance, and in this 

 connexion our opponents have cited especially the correspondence 

 between modifications acquired through use in the individual life- 

 time, and worked out through histonal selection, with the phyletic 

 transformations of the same parts. But it has been shown that 

 a number of parts which do not function actively at all, but only 

 passively, and thus cannot be caused to change through use, like the 

 hard skeletal parts of the Arthropods, vary phyletically in the same 

 certain and direct course as those which function actively, so that we 

 have every ground for assuming that there are other factors operating 

 in the transformation of the active as well as of the passive parts. 

 Finally, we discussed the last and strongest argument which has been 

 put forward in favour of the Lamarckian principle, that of co- 

 adaptation, that is, tlie simultaneous adaptation of many parts 

 co-operating in a common action, and we were able to contravert this 

 altogether by showing that exactly similar phenomena of co-adapta- 

 tion occur in systems of passively functioning parts, and further, that 

 they occur also among the workers of ants and bees, that is, in 

 animals which do not reproduce, and which, therefore, cannot transmit 

 the acquired results of exercise during their life. 



We therefore reject — and are compelled to reject — the Lamarckian 

 principle, not only on the ground that it cannot be proved correct, but 

 also because the phenomena, to explain which it is used, occur also 

 under circumstances which absolutely exclude any possibility of the 

 co-operation of this principle. 



SiLpplementary twte on the Transinissibility of Acquired 

 Functioiud Modifications. 



I cannot conclude this section without some reference to the 

 utterances of some naturalists who have quite recently attempted to 

 represent the inheritance of functional modifications as a conceivable 

 and even a necessary assumption. 



I may name first Ludwig Zehnder, a physicist who has wandered 

 into the domain of biology. In regard to the very facts which I have 

 adduced as evidence aga ind the existence of such inheritance, he has 

 endeavoured to show how we might conceive of them as having by 

 this very means arisen ^. 



He deals with the case of ants, that is to say, with the difieren- 



* Zehnder, Bie Entstehung des Lebens, Freiburg-i.-Br., 1899. 



H 2 



