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 Rotifera 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 XI 
ANIMAL MOTION, AND ITS INSTRUMENTS. 
_ 576. Tue 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- 
_ ‘Tiencing, 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- 
ay and ideas. Thus, if we find ourselves scorched by a flame, 
| we either withdraw our bodies from it, under the direction of 
E 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- 
), could do neither of these things. Again, it is entirely 
A 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 
hat 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. 
