PREFACE. 1 5 



of nerves, and an exponent, though scarcely distinguish- 

 able, of sensibility. In the snail, and muscle, the sepa- 

 ration of the fluid from the solid is more marked, yet 

 the prevalence of the carbonic principle connects these 

 and the preceding classes, in a certain degree, with the 

 vegetable creation. " But the insect world, taken at 

 large (says Mr. Coleridge) appears as an intense Life, 

 that has struggled itself loose, and become emancipated 

 from vegetation Florae liber ti, et liber tini!" In 

 insects we first find the distinct commencement of a 

 separation between the muscular system, that is, organs 

 of irritability, and the nervous system, that is, organs of 

 sensibility ; the former, however, maintaining a pre- 

 eminence throughout, and the nerves themselves being 

 probably subservient to the motory power. With the 

 fishes begins an internal system of bones, but these are 

 the results of a comparatively imperfect formation, being 

 in general little more than mere gristle. In birds we 

 find a sort of synthesis of the powers of fish and insects. 

 In all three, the powers are under the predominance 

 of irritability ; but sensibility, which is dormant in the 

 insect, begins to awaken in the fish, and, though still 

 subordinate, is quite awake in the bird, of which no 

 better proof can be given than its power of sound, with 

 the rudiments of modulation, in the large class of sing- 

 ing birds, and in some others a tendency to acquire and 

 to imitate articulate speech. The next step of ascent 

 brings us to the mammalia; and in these, including 

 beasts and men, the complete and universal presence of 



