2 The American Naturalist. [January, 



The views which I then defended have been recently 

 brought forward in almost parallel form, and without essen- 

 tial additions, by O. Hertwig (Zeit-und Streitfragen der Biologic, 

 I, Heft, D. 32-53) as arguments against the views of Weis- 

 mann. 



The second section is also directed against Weismann, for 

 it attempts to replace his conception of death by one more 



The third section is intended to make the significance of re- 

 juvenation clear, and at the same time, by a comparison of 

 larvse and embryos, to demonstrate a law of heredity which 

 has not been hitherto recognized. 



The Formative Force of Organisms. 



The assertion is safe, that the majority of biologists incline 

 at present to explain the forming of an organism out of its 

 germ upon mechanical principles. The prevalent conception 

 is that the forces of the ovum are so disposed that the evolu- 

 tion of the adult organism is the mechanical result of the pre- 

 determined interplay of those forces. The object of the pres- 

 ent article is to point out that this conception is inadequate, 

 and must be at least supplemented, if not replaced, by another 

 view, namely, that the formative force is a generally diffused 

 tendency, so that all parts inherently tend to complete by 

 their own growth and modification the whole organism— a 

 fact which finds a legitimate hypothetical expression in Dar- 

 win's Doctrine of pangenesis. The nature of the view here 

 advanced will become clearer upon consideration of the evi- 

 dence upon which it is based, and which is adduced below. 

 The evidence that the formative force is diffused through all 

 parts falls under three heads : 1. The process of regeneration 

 in unicellular and multicellular bionts ; 2. The phenomena of 

 of the duplication of parts ; 3. All forms of organic reproduc- 

 tion. Let us briefly consider these categories. 



1. Regeneration.— All living organisms have, to a greater or 

 less degree, the ability to repair injuries ; indeed, we must re- 

 gard the power of regeneration as coextensive with life, but 



