INTRODUCTION. XXV 



for making the organized beings at the foot 

 of the scale in either class a mass of irritable 

 matter formed by attraction, and a repulsive 

 principle to introduce into it and form a cel- 

 lular tissue, are the only ingredients necessary. 

 Mix them, and you have an animal which 

 begins to absorb fluid, arid move about as 

 a monad or a vibrio, multiplies itself by 

 scissions or germes, one of which being 

 stimulated by a want to take its food by a 

 mouth, its fluids move obediently towards its 

 anterior extremity, and in time a mouth is 

 obtained ; in another generation, a more 



talented individual discovering* that one or 







more stomachs and other intestines would be 

 a convenient addition to a mouth, the fluids 

 immediately take a contrary direction, and at 

 length this wish is accomplished ; next a 

 nervous collar round the gullet is acquired, 

 and this centre of sensation being gained, 

 the usual organs of the senses of course 

 follow. But enough of this. 



Let any one examine the whole organi- 

 zation and structure, both internal and ex- 

 ternal, of any animal, and he will find that it 

 forms a whole, in which the different organs 

 and members have a mutual relation and 



