322 AUGUST WEISMANN [april 



germ-plasm, and that it depends solely on the stimuli of position and the 

 nature of the particular cell-body itself, which of the many " Anlagen " 

 of the nuclear substance will undergo development. I may, indeed, 

 have laid too little emphasis on the role of the liberating stimuli, and 

 bestowed my attention too exclusively on the " Anlagen," but such an 

 extreme liberation-theory as that of Hertwig seems to me to overshoot 

 the mark on the other side. 



If what should be formed at a particular part of the organism 

 depended solely on the liberating stimuli, and the " Anlagen " were 

 everywhere the same, the same organ would necessarily invariably be 

 formed at any given place ; and it would be impossible that — as has 

 many times been observed — an antenna should grow out in place of 

 an insect's leg (Wheeler), or a leg instead of an antenna (Kraatz), or 

 that instead of an abdominal appendage in the common crab {Cancer 

 pagurus) a walking leg should appear (Bethe), or that antennae should 

 replace the amputated eye-stalks in shrimps (Herbst), or that four- 

 jointed tarsi should replace five-jointed ones (Bateson, Bordage). 



In regard to a few of these cases, one might seek to evade the 

 conclusion by the unverifiable statement that the liberating stimuli are 

 altered by the previous occurrence of injury. This may be so, but 

 still no explanation follows thereupon as to why, for instance, a four- 

 jointed tarsus is formed in place of a five-jointed one, since the four- 

 jointed tarsi of the ancestors did not result from amputation. I do 

 not see how it is here possible to avoid the assumption of different 

 " Anlagen " which can be liberated by a similar stimulus ; and thus 

 that the " Anlage " is the main thing and the stimulus only of more 

 general nature ; the stimulus only determining that something is to be 

 formed, the " Anlage " deciding what that something is. 



I hope to discuss this question more fully on some other occasion, 

 and therefore here only wished to indicate my position in regard to 

 some of the facts and opinions which have come to light since the 

 publication of the " Germ-Plasm." It will probably be necessary to 

 make a compromise between the theory of dispersal and that of 

 liberation, though it may not yet be possible even to sketch its outlines 

 with certainty. 



With regard, however, to the theory of regeneration, which is so 

 closely dependent on that of ontogeny, the explanation of the renewal 

 of a lost part is easy enough if we regard the complete germ-plasm as 

 present in every cell ; every " Anlage " could then come into operation 

 at any place if we assume their specific liberation-stimuli to be present. 

 But the effectiveness of the theory breaks down when we attempt to 

 explain why, nevertheless, regeneration in so many cases does not take 

 place ; — why, for instance, internal and external parts of the same 

 newt should behave so differently in this respect. If the injury 

 supplies the specific liberation-stimulus, why does it not liberate the 

 corresponding " Anlagen " in internal parts also ? There seems to be 



