EYES OF 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 Botifera and several Annelida, and also at the end of the 
arms of the Star-fish, red spots may he seen, which appear to 
he rudiments of eyes; hut no distinct organs of vision can he 
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 heen 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 he nearly as passive as are Plants,—expe¬ 
riencing, it is true, pain and pleasure from their sensations, 
hut 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. 
