48 THE FUNCTIONS OF LIFE. 



disappears altogether. We may often, however, 

 perceive some traces of its existence, but only in a 

 riuUmental state, and as if ready to be developed, 

 when the occasion may demand it. 



In the greater number of organic structures we 

 may trace a tendency to the repetition of certain 

 organs, or parts, and tlie regular arrangement of 

 these similar portions either round a central axis, 

 or in a longitudinal series. The former is apparent 

 in the verticillated organs of plants, and in the 

 radiated forms of zoophytes. The linear arrange- 

 ment is exhibited in the similar segments of annu- 

 lose and other articulated animals, and also in the 

 pieces which compose the spinal column ofverte- 

 brated animals. In these two latter classes, also, a 

 remarkable law of symmetry obtains in the forma- 

 tion of the two sides of the body, which exhibits 

 the lateral junction of similar but reversed struc- 

 tures. The violations of this law are extremely 

 rare ; yet some remarkable instances of anomalous 

 formations in this respect will hereafter be noticed. 



In treating of the particular functions of the 

 animal and vegetable economy I shall follow a dif- 

 ferent order from that in which I have presented 

 them in the preceding sketch. As the Mechanical 

 functions depend upon the simpler properties of 

 matter and the well known laws of mechanism, I 

 think it best to commence with the examination of 

 these. Our attention will next be directed to the 

 highly interesting subjects which relate to the Nu- 

 tritive or Vital functions both of vegetable and 

 animal structures : for as they involve the chemical 

 properties of organized substances, and are, there- 

 fore, of a more refined and intricate nature than the 



