I2 6 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



the after-image is of a complementary color. Red is seen 

 as green and vice versa; blue as orange-yellow and vice 

 versa. But ' to discuss these color phenomena would 

 carry us too far. 



Generalization of these Facts. — We have seen 

 that all changes or variations of whatever kind in the 

 retina, whether images of objects, or shadows, or brands, 

 show themselves as appearances in space. Therefore 

 space itself as perceived by the eye is an exter?ialization or out- 

 ward reference of retinal states. With the eyes open, the 

 field of view crowded with objects is the externalization 

 of the stimulated retina crowded with images; with the 

 eyes shut, the field of darkness is still the externalization 

 of the unstimulated retina. The sense of space before 

 the eyes is ineradicable. We can not rid ourselves of it. 

 In the dark or with the eyes shut it is still there, as the 

 field of darkness. It is in front, not behind the head. 

 It is a positive appearance, which may be roughly out- 

 lined and may be described. It is not black, but rather 

 dark-gray or brown, with confused markings and cloud- 

 ings and sometimes colored spaces scattered through- 

 out. Thus we have an abiding sense of space as the ex- 

 ternal representative of the retina, even though we see 

 no object in it, precisely as we have an abiding sense of 

 a hand, even though we feel nothing with it. 



The Second Law of Vision ; the Law of Direc- 

 tion. — The previous law asserts the perception of space 

 as the externalization of retinal states, and therefore the 

 reference of all retinal images to that space. This law 

 gives the direction of the external reference. In several 

 of the preceding experiments we have alluded to their 

 general direction. We come now to define it exactly. 



The law may be given thus: Any impression on a 

 rod or cone of the bacillary layer is referred by the rod 

 or cone back into space end on — i. e., at right angles to 



