PART IV 



Histogenesis and Morpno^enesis 

 or tne Or^an-Systems 



For definitions of cytogenesis, histogenesis, etc., see Chap. 11; for histogenesis and 

 morphogenesis of the organ systems, see Chaps. 12-21. The events described in Chapters 

 12-21 occur, to a great extent, during the so-called larval period or period of transition. 

 During this period of development, the basic conditions of the various organ-systems 

 which are present at the end of primitive embryonic body formation are transformed 

 into the structural features characteristic of definitive or adult body form. In other 

 words, during this phase of development, the basic, generahzed morphological conditions 

 of the various organ-systems of the embryo are rearranged and transformed into the 

 adult form of the systems. As a result, the body as a whole assumes the definitive or 

 adult form. 



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