Heredity. 157 



(1) "Acquired characters are those which result from ex- 

 ternal influence upon the organism, in contrast to such as spring 

 from the constitution of the germ." 



(2) " Characters can only be inherited in so far as their rudi- 

 ments (Anlagen) are already given in the germinal protoplasm 

 (Keimplasma)." 



(3) " Modifications which are wrought upon the formed body, 

 in consequence of external influences, must remain limited to 

 the organism in which they arose." 



(4) " So must it be with mutilations, and with the results of 

 use or disuse of parts of the body." 



(5) "No such modifications of the body (affected by environ- 

 ment or by use and disuse) can be transmitted to the germ- 

 cells, from which the next generation springs. They are, 

 therefore, of no account in the modification of the species." 



(6) " The only principle that remains for the explanation of 

 the modification of the species, is direct germinal variation." 

 " The intermingling of the sex elements is the origin of the 

 variations on which natural selection in the usual way operates." 



Weismann's position is thus clear and definite. The 

 sole fountain of specific change is found in the germ- 

 plasm of the sex-cells. The environment does make 

 dints upon the organism, but only upon its body; the 

 reproductive cells, through which alone the variation 

 could be transmitted, are either unaffected or are not 

 affected in such a specific way as to bring about the 

 transmission of the acquired character. The effects of 

 use and disuse may be marked enough, and important 

 for the individual, but they are not transmitted, and 

 therefore of no account in the history of the species. 

 The ground is taken from under the feet of Lamarckians 

 and Buffonians, and the whole burden of progress is 

 laid upon germinal variation and natural selection. 



(i) Various naturalists have brought forward what 

 appear to them to be examples of the genuine trans- 

 mission of individually-acquired characters. Cr i ticismso f 

 Thus Detmer and Hoffmann among botan- Weismann's 

 ists, and Eimer among zoologists, may be Posltlon - 

 quoted. The latter especially gives numerous examples 

 to prove the untenability of Weismann's position. To 

 some of the instances urged against him, Weismann 

 has replied; but as each case has to be carefully tried 

 on its own merits, and as sufficient decisive experiments 



