CHAPTER LXIX 

 THE SENSE OF VISION 



SECTION I 



The Receptor Mechanism. The perception of the rapid undula- 

 tions of the ether is usually confined to specialized nerve cells, the 

 visual cells. Some low forms of life have a rudimentary eye or eye- 

 spot (Fig. 336, e). The visual cells may be scattered over the body 



Fio. 330. INDIVIDUAL FLAGELLATE CHLAMYDOMOSAS RETICULATA. (Redrawn from 



Dahlgren and Kepner.) 



e, Eyespot with pigment and lens; nu., nucleus; c. v., contractile vacuole. X 1,000. 



surface, but usually are aggregated together with accessory tissues to 

 form a specialized organ of vision, the eye. Various complicated 

 forms of eyes are described among the invertebrates. In the 

 higher animals the receptor mechanism for vision is contained 

 in the retina, the delicate nervous layer lining the posterior portion 



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