CHAPTER TWELFTH. 



METAMORPHOSES OF ANIMALS. 



5-18. UNDEE the name of metamorphoses are included those 

 changes \vhicli 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. 



5-49. 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 woody layers to the trunk. In animals the whole 

 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 

 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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