

CHAPTER TWELFTH. 



METAMORPHOSES OF ANIMALS. 



548. UNDEE, the name of metamorphoses are included those 

 changes which the body of an animal undergoes after birth, 

 and which are modifications, in various degrees, of its organ- 

 ization, form, and mode of life. Such changes are not pe- 

 culiar to certain classes, as has been so long supposed, but 

 are common to all animals without exception. 



549. Vegetables also undergo metamorphoses, but with 

 this essential difference, that in vegetables the process consists 

 in an addition of new parts to the old ones. A succession of 

 leaves, differing from those which preceded them, comes on 

 each season ; new branches and roots are added to the old 

 stem, and woodv layers to the trunk. In animals the whole 



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body is transformed, in such a manner that all the existing 

 parts contribute to the formation of the modified body. The 

 chrysalis becomes a butterfly ; the frog, after having been 

 herbivorous during its tadpole state, becomes carnivorous, 

 and its stomach is adapted to this new mode of life ; at the 

 same time, instead of breathing by gills, it becomes an air- 

 breathing animal, its tail and gills disappear, lungs and legs 

 are formed, and finally it lives and moves upon the land. 



550. The nature, the duration, and importance of meta- 

 morphoses, and also the epoch at which they take place, are 

 infinitely varied. The most striking changes naturally pre- 

 senting themselves to the mind, when we speak of meta- 

 morphoses, are those occurring in insects. Not merely is 

 there a change of physiognomy and form observable, or an 

 organ more or less formed, but their whole organization is modi- 

 fied. The animal enters into new relations with the external 

 world, while at the same time, new instincts are imparted to it. 

 It has lived in water, and respired by gills ; it is now furnished 

 with tracheae, and breathes air ; it passes by with indifference 

 objects which before were attractive, and its new instincts 

 prompt it to seek conditions which would have been most per- 



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