176 G. E. COGHILL 



fibers a considerable time before the embryo can respond to 

 tactile stimulation. 



10. The dorso-ventral distribution of the cells of the column 

 is definitely correlated with the position of the mesoderm. 



c. The giant ganglion cells as peripheral nerves 



Certain results of my physiological experiments, which will be 

 described in the physiological part of this paper, have required, 

 for their explanation, a critical study of the peripheral relations 

 of the giant ganglion cells, since the dendritic process of these 

 cells constitute the afferent peripheral system of the trunk 

 during the period under investigation. 



For the illustration of these relations drawings have been made 

 with the Bausch and Lomb drawing apparatus at a magnification 

 of 940 diameters and reduced to 470 in figures 1 to 27 and 27a. 



(1) The relation of the giant ganglion cells to the skin. The re- 

 lations of these cells to the skin is illustrated particularly in figures 

 8, 15 to 21, 24 and 25. 



Figure 8 is taken' from a series of horizontal sections, but 

 at this level of the cord the section is obUquely transverse 

 with the dorsal portion pitched caudad. It represents a ganglion 

 cell fiber in the space between the last two myotomes in a non- 

 motile embryo. Here a large fiber, with a broad conical base 

 coming out of the cord, at the latero-dorsal angle, reaches directly 

 to the skin. Its area of attachment is upon the thickened region 

 of the skin that characteristically projects in between the myo- 

 tomes. There is evidence of its branching immediately beneath 

 the skin and having at least two terminals. 



Figures 15 to 17 are drawn from three successive sections of 

 a transverse series. They represent a fiber in the myoseptum 

 between the thirteenth and fourteenth myotomes of an embryo 

 of the non-motile stage. The particularly significant relations 

 here are between the fiber and the myotome as the fiber leaves 

 the cord, the intimate contact with myotomes as the fiber passes 

 between them and the pseudopodial branching of the fiber im- 



