GENESIS, HEREDITY, AND VARIATION. S7S 



in the microscopic head of a spermatozoon ! Hardly a credi- 

 ble supposition. Nor is it easy to see how we are helped by 

 the hypothesis of constitutional units. Take the feather in 

 its budding state and ask how the group of such units, alike 

 in structure and perpetually multiplying while the unfolding 

 goes on, can be supposed by their mutual actions so to affect 

 one another as eventually to produce the symmetrically-ad- 

 justed processes which constitute the terminal eye. Imagina- 

 tion, whatever licence may be given, utterly fails us. 



At last then we are obliged to admit that the actual organ- 

 izing process transcends conception. It is not enough to 

 say that we cannot know it; we must say that we cannot 

 even conceive it. And this is just the conclusion which 

 might have been drawn before contemplating the facts. For 

 if, as we saw in the chapter on " The Dynamic Element in 

 Life," it is impossible for us to understand the nature of this 

 element — if even the ordinary manifestations of it which a 

 living body yields from moment to moment are at bottom 

 incomprehensible; then, still more incomprehensible must be 

 that astonishing manifestation of it which we have in the 

 initiation and unfolding of a new organism. 



Thus all we can do is to find some way of symbolizing the 

 process so as to enable us most conveniently to generalize its 

 phenomena; and the only reason for adopting the hypothesis 

 of physiological units or constitutional units is that it best 

 serves this purpose. 



