544 CHARLES R. STOCKARD 



From this it would seem as though the material of the chro- 

 matophore had lost its contractile or wandering power after 

 once becoming arranged around the yolk vessels. Those black 

 chromatophores which retain their cellular individuality along 

 the borders of the pericardial space also fail to contract when 

 treated with KCl or adrenalin. 



Although this physiological test failed to serve the purpose 

 for which it was used I feel certain, after many observations, 

 that the black chromatophores actually do form true syncytial 

 masses as they surround the vessels. 



b. The brown type chromatophore. The brown chromato- 

 phores differentiate on the yolk-sac at about the same time as 

 the black. They are always somewhat smaller and more deli- 

 cately formed cells than the black, and react in a slightly differ- 

 ent manner. Figures 22 and 26 show several brown chromato- 

 phores before the end of the third day. They are paler in 

 appearance and more elongate in shape than the black cells. 



The two types of cells are well contrasted in figures 11, 12 and 

 13 referred to above. The brown cell is smaller, with more deli- 

 cate processes and is the more rapidly moving of the two. The 

 three figures indicate its condition in embryos of 72 hours. 



These pigment cells also wander to the vessel walls and yolk 

 spaces and take on their permanent condition about the fifth 

 day. Figure 16 illustrates one of the exquisite brown pigment 

 cells in a yolk-sac of 5 days. The nucleus is still distinguishable 

 in life while it is not in the black cells of this age. The mossy 

 branched processes projecting from all sides give to this cell a 

 most fascinating form. 



Fig. 14 A camera lucida drawing of two huge black chromatophores lying 

 upon a yolk vessel of a 5 day embryo. The adjacent sides of the chromatophores 

 are beginning to fuse to form a syncytium. The direction of blood flow is indi- 

 cated by the arrows. 



Fig. 15 A syncytial mass of black chromatophores forming a sheath about 

 the vitelline vessels. The chromatophores become so thin that the pigment 

 granules are spread apart giving a less intense color. The individual cells are 

 completely lost in the syncytium (3b. DD. ob.). 



