516 



Special Vertebrate Organogenesis 



CONCLUSION 



From the foregoing it is evident that the 

 skin of vertebrates is a complex organ com- 

 posed of a variety of tissue elements and, 

 like other organs and organ systems, pro- 

 gressively increases in diversity during 

 ontogeny. Tissue interrelationships appear to 

 play a vital role in its organization and 

 differentiation. Within recent years infor- 

 mation has been obtained concerning the 

 temporal and spatial restriction of develop- 

 mental potencies of the skin ectoderm and 

 cellular reactions between it and the under- 

 lying mesodermal layer in bringing about 

 regional specialization in the skin and its 

 various derivatives. At the present time lit- 

 tle is known about intrinsic, qualitative dif- 

 ferences among integumentary cells that are 

 revealed only by their particular methods 

 of response to various types of stimuli, both 

 internal and external. It is highly probable, 

 however, that through continued and con- 

 certed experimental attack and the use of 

 new and sensitive biophysical and biochemi- 

 cal methods it may yet be possible to obtain 

 definite knowledge of the nature of these 

 intrinsic qualities and thus increase our 

 understanding of how they fit into the pat- 

 tern of developmental organization of the 

 skin and its diverse derivatives. 



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