24S ORGANS OF THE SENSES. 



bodies directly applied to the skin, or from sapid bodies dis- 

 solved in the secretions of the mouth, or from odorous ema- 

 nations diffused through the surrounding element, or from 

 simple undulations of that element reaching the surface of 

 the body, or from those finer vibrations which constitute the 

 phenomena of light. There may be many other kinds of 

 impressions derived from outward bodies, for which the 

 sensitive nerves of the lower animals are adapted, besides 

 those which affect us, and we cannot always be certain of 

 the identity of the feelings communicated to them by organs 

 which appear analogous to our own. Although we often 

 cannot detect distinct organs for the senses which we ascribe 

 to the lower animals, these organs are commonly enumerated 

 according to the supposed generality of their function in 

 the animal kingdom, from the most general feeling of the 

 nervous system, or the sense of touch to that of vision or of 

 hearing, but the most general organ of sense perceptible in 

 animals, as superadded to the nerves of feeling already de- 

 scribed, is that of vision which relates to light, so universally 

 diffused through nature, and so influential on both kingdoms 

 of organized beings and even on the constitution and proper- 

 ties of unorganized bodies. 



SECOND SECTION. 



Organs of Vision. 



Many animals, like plants, are affected sensibly by light, 

 without their exhibiting either organs of vision or a single 

 filament of nervous matter. As plants, guided by light, open 

 and close their flowers and their leaves, or follow with their 

 expanded flowers the diurnal course of the sun, or seek his 

 light with their slow-moving branches and their leaves with- 

 out a perceptible nervous system, so we observe the nerve- 

 less gemmules of poriferous animals, and of zoophytes guided 

 by the same agent in selecting a proper place for fixing and 

 developing ; the hydra, without eyes or nerves, uniformly 

 moves to the light, the eyeless actinia shuns its influence, 

 and many zoophytes expand or contract their whole body 



