1896] loJ [Ortmann. 



The process of inheritance is most obscure.* We Icnow nothing of 

 the causes of inlieritauce or — perhaps it is better to say — of non-inheritance 

 often occurring. Weismann's theory of inheritance, even if we accept it 

 (as I do not), does not explain the essence of heredity : it merely refers 

 inheritance to minute processes in fertilization. But this knowledge that 

 heredity is due to the peculiarities in propagation is a very old one, as 

 old as modern zoology and perhaps even older, and more accurate knowl- 

 edge of the minute details in propagation, and their arbitrary augmenta- 

 tion by supposed complications does not promote our understanding of 

 heredity. Yet we do not know how the "tendencies of inheritance " of 

 the germs (or parts of the germs) are. transferred to the "soma" of the 

 descendants; we do not know how the germs get these "tendencies" 

 from the "soma" of the parents ; we do not know why certain "tenden- 

 cies " become visible in the descendants, while others do not ; we do not 

 know what a "tendency of inheritance " is like anyhow. f A theory of 

 inheritance has to endeavor to answer the questions put here, otherwise 

 it does not explain anything, and the essence of heredity continues to be 

 as obscure as before. 



By inheritance and repeated action of particular external conditions a 

 distinct direction of variation may be induced : certain animal forms tend 

 again and again to vary in the same direction, and the degree of the varia- 

 tions is thus increased. This process is what Eimer calls orthogenesis, 

 and if the action of the external conditions as well as of inheritance is 

 not a steady one, but interrupted and irregular, we have his halmatogen- 

 esis. Both terms clearly come under the head of inheritance. Ortho- 

 genesis and halmatogenesis can eft'ect " mutations," but we must bear in 

 mind that here no principle of utility comes into play. 



It is well to be noted that the two factors mentioned, variation and 

 inheritance, act only upon single individuals. They act often upon a 

 number of individuals in the same or analogous manner, but each individ- 

 ual can vary and inherit without regard to others. The tw^o following 

 principles (natural selection and separation) can only act upon a multi- 

 tude of individuals simultaneously, and their action becomes conspicuous 

 only by the comparison of many individuals. 



3. Upon the material produced by variation and inheritance acts a third 

 factor: Natural Selection. By this principle all variations injurious in 

 the struggle for existence, all the forms not fitted for existence under a 



*See Osborn ("The Hereditary Mechanism and the Search for the Unknown Factors of 

 E%'olution," £iV. Led. Mar. Biol. Lab., Wood's Holl, 1895): " If acquired variations are 

 transmitted tliere must be some unknown principle in heredity." 



fOf course, Weismann has tried to answer these questions, at least partly, by his " theo- 

 ries," but such questions cannot be explained at all by " theories," the very foundations of 

 which are either disputable or arbitrary, or even illogical and contrary to the known facts. 

 On the whole, Weismann's arguments run in a perfect circulus viliosus. His theory of inher- 

 itance is founded upon the belief that acquired variations are not transmitted, and tlie 

 demonstration, that acquired variations are not transmitted, is founded upon the belief 

 that his theory is correct (comp. Keue Gedanken zur Vererhungsfrarje, 1895, pp. 11 and 21). 



