458 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



that there could be no question of imperative divisions 

 separating the germ-plasm into right and left halves, 

 and so forth, but that the method of division was de- 

 termined by pressures and relative gravities. Altera- 

 tion of these made the ova divide into novel but sym- 

 metrical forms. Chabry obtained normal embryos in 

 cases where some of the segmentation-spheres had 

 been artificially destroyed. 



''These cases all show that in its possibilities each 

 segmentation-sphere is identical ; that as a result of 

 heirs-equal division, each cell contains all the material 

 necessary to cause the development of a complete em- 

 bryo. Weismann would have to suppose that in all 

 these cases, in addition to its half of the nuclear mat- 

 ter resulting from heirs-equal division, it had also a 

 stock of unaltered germ-plasm ready to be called into 

 activity by unwonted stimuli. But even this hypothesis 

 would not account for cells distorted by compression 

 responding with the production of unwonted symme- 

 tries." 



6. OBJECTIONS TO THE DOCTRINE OF INHERITANCE 

 OF ACQUIRED CHARACTERS. 



I will now mention some objections to the theory 

 of epigenesis, or the inheritance of acquired charac- 

 ters. Some of them appear at first to have consider- 

 able force, but the explanations which have been of- 

 fered seem to me to be sufficient. 



Weismann's merit consists in having directed at- 

 tention to the isolation and continuity of the germ- 

 plasma, factors which must be taken account of in any 

 theory of inheritance. The continuity of reproductive 

 function which this substance displays is a fact of great 



