THE VERTEBRATE BODY 



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make the proper connections through the brain, but when a stimulation 

 is strong enough, the response will be more rapid due to the principle of 

 reflex action. A person suddenly sitting on a pin does not take time to 

 reason out what has happened before responding ; the stimulation is so 



Photos by Winchester 



Fig. 22.16. Diagram illustrating nearsighted and farsighted vision. The black lines 

 represent rays of light originating from a distant point of light. The lens of the near- 

 sighted person focuses these rays at a point in front of the retina and they spread out 

 again to give a fuzzy image on the retina. However, when an artificial minus lens is 

 placed in front of the eye the rays are spread slightly before reaching the lens of the 

 eye and they come to a sharp focus on the retina. In the farsighted individual the rays 

 reach the retina before they have come to a focus and, again, a fuzzy image results. 

 In this case a plus lens may be put in front of the eye ; this causes a slight convergence 

 of the rays and a sharp focus on the retina. 



