EBEN J. CAREY 81 



tend to pursue a straight line if the factors of resistance due to differ- 

 ential growth did not interfere. An exception to this would be found 

 in the spiral type of cleavage observed by Child in Arenicola cristata, 

 and Wilson in Nereis. In these forms the rotation of the cells appears 

 to be predetermined in the parent cells, as is proved by the position 

 of the spindles and by the form of division. In the intestine the 

 inner curved surface of the mesenchymal wall constantly deflects the 

 mitotic path in a circular manner. This would impart the rotary 

 elem.ent to the compound spiral motion of growth. 



The relation of the pharynx to the esophagus and of the rectum to 

 the colon is comparable to that of the wide and narrow components of 

 a funnel. A stream running down the inclined wall of the wide ele- 

 ment would be deflected in a rotary manner so that its progression 

 through the narrow integer would be in the manner of a helix. The 

 determination of a left- or right-handed helix would depend upon the 

 initial direction of impelling the stream. 



The direction of epithelial growth in a left-handed helix has a defi- 

 nite mechanical basis in the intestine, but as yet is undetermined. 

 The epithelial growth is roughly comparable to the stream exemplified 

 above; i.e., the glass of the funnel to the mesench5nTie. The initial 

 impulse of the water pressure is comparable to that of growth. This 

 causes the rectilinear motion of progression. The circular resistance 

 of the glass is analogous to that of the mesenchyme. This causes a 

 deflection of the rectilinear motion in a rotary manner, the two char- 

 acterizing the helicoidal motion of the intestine. 



CONCLUSIONS. 



Esophageal Development. 



1. The region of most active mitosis per mm. of cross-section in the 

 esophagus is the entodermal epithelial tube. The mitotic figures 

 follow a spiral path in the manner of a left-handed helix from the 

 cephalic to the caudal direction. 



2. The region of least active growth per mm. of cross-section in the 

 esophagus is the mesenchyme surrounding the epithelial tube. 



3. The hehcoidal activity of the epithelial tube causes a vortical 

 reaction in the surrounding mesenchyme. The mesench3rmal whirl- 

 pool represents a reaction to the spirally growing epithelial tube. 



