594 ANIMAL PHYSIOLOGY. 
follow. Thus, stimulation of the right side of the nates leads 
to movements of both eyes to the left, and the reverse when 
the opposite side is stimulated; algo, 
stimulation in the middle line causes 
convergence and downward move- 
ment, etc., with the corresponding 
movements of the iris. Since section 
of the nates in the middle line leads 
to movements confined to the eye of 
the same side, the center would ap- 
Fie. 435.—Diagram to illustrate de- pear to bedouble. However, it may be 
fie coumiaure of icat ote that the cells actually concerned do 
ames not lie in the corpora quadrigemina, 
but below, or outside of them. The localization is as yet in- 
complete. 
The Horopter.—If we hold up one finger before another, in 
front of both eyes, when the accommodation is made for the 
one the other will appear double, owing to the images not fall- 
ing on corresponding parts of the retina; for, if one eye.be 
closed, one of the images disappears. 
Another way of putting the matter is, to say that the objects 
in the field under consideration do not lie in the horopter. The 
A 
Fie, 436.—The horopter (after Le Conte). When the eyes are directed to the point A in the 
circle, images from any other part of it (as D) fall on corresponding points of the retine. 
latter is that arrangement of points in space from which rays 
fall on corresponding (identical) parts of the retina. It must 
