ABSTRACT
Our belief about visual system as functional tool providing only image formation, and in a common sense an interpretative depiction of the surrounding real world,has been drastically changed by recent (and old but revised)achievements onnonimage-forming vision,more widely termed as nonvisual photoreceptionornonvisualphotosensitivity(NVPforboth).Classicalstudiesininvertebrateandlower vertebrate species have described,namely,at time,extra ocularor extraretinal photo sensitive cells which exerted an ancillary role to obvious eye-like structures in mere detection of environmental irradiance(oneforalltheso-called thirdeye,i.e.,the pineal gland,of lower vertebrate organisms).Such role assumes remarkable importance in those animals that lack obvious eyes or with poor optical apparatus.
