CHAPTER X 



VON BAER AND THE RISE OF EMBRYOLOGY 



Anatomy investigates the arrangement of organic tissues ; 

 embryology, or the science of development, shows how they 

 are produced and arranged. There is no more fascinating 

 division of biological study. As Minot says: " Indeed, the 

 stories which embryology has to tell are the most romantic 

 known to us, and the wildest imaginative creations of Scott 

 or Dumas are less startling than the innumerable and almost 

 incredible shifts of role and change of character which 

 embryology has to entertain us with in her histories." 



Embryology is one of the most important biological sci- 

 ences in furnishing clues to the past history of animals. 

 Every organism above the very lowest, no matter how com- 

 plex, begins its existence as a single microscopic cell, and 

 between that simple state and the fully formed condition 

 every gradation of structure is exhibited. Every time an 

 animal is developed these constructive changes are repeated 

 in orderly sequence, and one who studies the series of steps 

 in development is led to recognize that the process of 

 building an animal's body is one of the most wonderful 

 in all nature. 



Rudimentary Organs. — But, strangely enough, the course 

 of development in any higher organism is not straightforward, 

 but devious. Instead of organs being produced in the most 

 direct manner, unexpected by-paths are followed, as when 

 all higher animals acquire gill-clefts and many other rudi- 



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