EBEN J. CAREY 361 



section (Figs. 1 to 9). This region was found to change at different 

 levels of the serial sections. By graphic reconstruction this plot was 

 found to form the path of a definite spiral. The predominant type was 

 the left-handed helix. In one of the embryos of the twenty that were 

 plotted this spiral v/as arranged as a right-handed helix (Figs. 1 

 to 9). The spiral itself presented a head or apical region in which 

 mitotic figures were found to be numerous, and a tail or basal end in 

 which there were fewer and fewer figures. The apical end of the 

 spiral path is always directed towards the ileocecal valve and the basal 

 end towards the rectum. Growth is, therefore, from below upwards 

 in a spiral course. One spiral growth is quickly followed by a second 

 which rifles a path slightly lateral to its predecessor. This in turn is 

 followed by a third in a path still more lateral, and so on around the 

 circumference. This intermittent rhythm of explosive spiral growth 

 may be compared to that of the successive fire balls emitted by a 

 roman candle in fireworks. The paths formed by this explosive 

 spiral growth may be compared to those within the barrel of a Win- 

 chester rifle. 



The most rapidly growing part of the intestine, therefore, is the 

 epithelial tube. In embryos 10 to 25 mm. in length the descending 

 colon grows relatively more rapidly in diameter than in length (Tables 

 I and II). The increase in diameter is due primarily to the rapid 

 growth of the entodermal epithelial tube and only partially to its 

 surrounding mesenchymal cloak. The latter is relatively passive in 

 growth with respect to the former (Fig. 10) . It is during this early 

 increase in diameter that the inner smooth muscle coat is in proc- 

 ess of formation. The mesenchymal cells are drawn out gradually 

 in a definite series of concentric rings. These rings appear not unlike 

 those of the planet Saturn and the annular nebula in Lyra. 



A definite centripetal force is active in the rapid spiral growth of the 

 intestinal epithelial tube. The surrounding mesenchymal cells are 

 thrown into an obvious series of concentric rings, according to their 

 various densities. Those possessing the greatest density will join the 

 outer ring in the tangential path of the force, whereas the inner ring 

 will be composed of bodies forming a gradient of decreasing densities. 

 The cells forming the outer ring wiU be most elongated. 



