EYES OP MOLLUSKS, ETC. ANIMAL MOTION. 443 



the Mollusca which possess a head namely, in the Gastero- 

 pods, Pteropods, and Cephalopods ; those of the last class 

 present an evident approach to the eyes of Fishes, in the 

 greater completeness of their structure, and in their adapta- 

 tion for distinct vision. In many of the lower Mollusca, as in 

 the Eotifera and several Annelida, and also at the end of the 

 arms of the Star-fish, red spots may be seen, which appear to 

 be rudiments of eyes ; but no distinct organs of vision can be 

 seen in the Zoophytes and lowest Mollusca ; although many 

 of them appear very sensible to the action of light. 



CHAPTER XII. 



ANIMAL MOTION, AND ITS INSTRUMENTS. 



576. THE different modifications of the faculty of Sensation 

 which have been described in the preceding chapter, enable 

 Man and other Animals to become acquainted with what is 

 going-on around them. But their connexion with the external 

 world is not confined to this faculty ; for if they possessed it 

 alone, they would be nearly as passive as are Plants, expe- 

 riencing, it is true, pain and pleasure from their sensations, 

 but not having the power of avoiding the one or of procuring 

 the other. They are endowed, however, with another faculty, 

 that of spontaneous movement ; which serves the double 

 purpose of enabling them to act upon the inanimate world 

 around them, and of communicating to each other their feel- 

 ings and ideas. Thus, if we find ourselves scorched by a flame, 

 we either withdraw our bodies from it, under the direction of 

 the instinct which leads us to avoid suffering, or we set about 

 to extinguish the fire by an act of the will, founded upon our 

 rational knowledge of its injurious tendency. The Plant, 

 even if it had sensation (which some naturalists have sup- 

 posed), could do neither of these things. Again, it is entirely 

 by the movements concerned in speech, by those giving 

 expression to the countenance, and by the gestures of the 

 body, that we convey to beings like ourselves a knowledge of 

 what is passing in our own minds ; of this power we know 

 that plants are entirely destitute, and it is possessed in a very 

 limited degree by the lower Animals. 



