302 DARWINISM STATED BY DARWIN HIMSELF. 



modifications. It is equally or even more unintelligible, 

 on any ordinary view, how the effects of the long-contin- 

 ued use or disuse of a part, or of changed habits of body 

 or mind, can be inherited. A more perplexing problem 

 can hardly be proposed ; but on our view we have only 

 to suppose that certain cells become at last structurally 

 modified, and that these throw ofE similarly modified 

 gemmules. This may occur at any period of develop- 

 ment, and the modification will be inherited at a corre- 

 sponding period ; for the modified gemmules will unite 

 in all ordinary cases with the proper preceding cells, and 

 will consequently be developed at the same period at 

 which the modification first arose. With respect to 

 mental habits or instincts, we are so profoundly ignorant 

 of the relation between the brain and the power of 

 thought that we do not know positively whether a fixed 

 habit induces any change in the nervous system, though 

 this seems highly probable ; but, when such habit or other 

 mental attribute, or insanity, is inherited, we must be- 

 lieve that some actual modification is transmitted ; and 

 this implies, according to our hypothesis, that gemmules 

 derived from modified nerve-cells are transmitted to the 

 offspring. 



NECBSSAET ASSUMPTIONS. 



Pafe 869 ^ ^^^® °°^ enumerated the chief facts 

 which every one would desire to see connected 

 by some intelligible bond. This can be done, if we make 

 the following assumptions, and much may be advanced 

 in favor of the chief one. The secondary assumptions 

 can likewise be supported by various physiological con- 

 siderations. It is universally admitted that the cells or 

 units of the body increase by self-division or proliferation, 

 retaining the same nature, and that they ultimately be- 



