532 ROSS G. HARRISON 



tened than in the other case. A comparatively thin fringe of 

 cells has formed around it and many cells have left the mass 

 entirely, being scattered at various distances from the latter. 

 These cells are at two levels. The upper layer is in contact with 

 the lower surface of the cover-slip, where the outwandering cells 

 are apt to assume a polygonal form, though they are sometimes 

 influenced by the web fibers attached to the cover. In the 

 lower layer the cells are arranged with reference to the web 

 fibers, and they are usually drawn out into long processes which 

 are closely applied to the latter (see also figs. 4 to 7). 



The preparation shown in figure 3 is from Series IV, being one 

 of those mounted in Locke's solution. It shows the effect of 

 contact with the smooth cover-slip only. The drawing was 

 made about forty-five hours after the culture was prepared. 

 The tissue consisted of a piece of the medullary cord with some 

 mesoderm and a small piece of the notochord attached. It has 

 been flattened in pancake form against the cover-slip by the 

 spreading of the drop of fluid. A small number of isolated 

 polygonal cells have moved off upon the cover, and a thin fringe 

 of cells surrounds the tissue as in the preceding case. 



The adaptation of the cells to the web fibers is shown more 

 clearly in figures 4 to 7, which are all taken from the same series 

 of experiments. Figure 4 shows a cell with two hyaline processes 

 attached to the web fibers running approximately at right angles. 

 Figure 5 shows two bipolar and a tripolar cell, drawn when the 

 preparation was two days old, figure 6 two cells from an eight 

 day culture, and figure 7 pigment cells from another preparation 

 of six days. The pigment is of two kinds, a granular black 

 melanin and a diffuse yellow pigment (probably a lipochrome) 

 present in two of the cells in large quantities. The yellow cells 

 contain a little of the dark granular pigment, though much less 

 than the other cells, and the latter contain none of the yellow. 



Nerve fibers developed in only a few of the cases and in 

 none of these was anything notable shown. All of the nerves 

 observed were growing upon the surface of the cover slip. The 

 web fibers do not seem to be a favorable support for them. 



