378 



THE AMERICAN NATURALIST [X'ol. XLI 



to act as 'conductors or resonators,' a fact which would not exckide 

 chemical changes resulting in fatigue. The long fibrils respond 

 to the red end of the spectrum and the short ones to the blue. In 

 Mjual length and only monochromatic vision 

 ; their varying length allows a range of 

 )n in the form or dimensions of 

 the cones would bring about cor- 

 responding changes in vision. 

 The increased length of the 

 cones at the fovea provides for 

 a greater power of color discrim- 

 ination. If the base of a cone 

 were absent or cylindrical it would 

 be red blind. 



This theory is illustrated in fig- 

 ure 6. On the right is the dia- 



tlie latter radiate from an axial 

 lilament, the existence of which 

 has been discussed and denied 

 by other investigators. The fi- 

 brils in the right half of the cone 

 are drawn as responding to red, 

 yellowish green, and violet light; 

 the Young-Helmholtz curves are 

 shown on the left. In nonpolar- 

 ized light all of the fibrils in a 



spond uniformly, but in polarized 

 liiiht only such are effected as are 

 I the left of the figure. Thus the 

 ,,hmu-.l. The correctness of this 



It will be noted that 

 theories the mechanism 

 a single cone. The lie 



