70 



DYNAMICS OF HISTOGENESIS. II 



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Fig. 15. Curves of differential growth of the epithelial tube and mesen- 

 chyme of the esophagus. Since there is no restricting peritoneal menibrane in 

 the lower cervical region of the esophagus the more rapid rate of growth of the 

 epithelial tube over that of the mesenchyme is not as definite as that seen in the 

 descending colon. The great extent of mesenchymal area is due to the centri- 

 petal force of the epithelial tube. The centrifugal reaction tends to throw the 

 cells off tangentially. Consequently, the greater area of the mesenchyme is 

 not due to an intrinsically more rapid rate of mitosis over that found in the 

 epithelial tube but to the radial force (centrifugal force) of the mesench>-me in 

 reaction to the centripetal force of the epithelial tube. 



