No. r.] PHYSIOLOGY OF COLORATION IN ANIMALS. 163 



The blood vessels now have a covering of pigment which, 

 however, is not uninterrupted, but shows many shorter or 

 longer open spaces where the vessel is entirely free from 

 pigment. It seems that the chromatophore remains at that 

 point of the blood vessel to which it originally crept. 



3. Therefore the history of coloration of the yolk sac in 

 the Fundulus embryo seems to be as follows : The production 

 of chromatophores takes place with the exception of a few 

 spots in almost every part of the yolk sac. Whether the pro- 

 duction of pigment and the origin of chromatophores is in 

 some way dependent upon the formation of the blood and the 

 blood vessels I cannot say ; but as a matter of fact the chro- 

 matophores make their appearance at almost every point of the 

 surface regardless of the blood vessels. As soon as a process 

 of the chromatophores reaches the blood vessel the whole mass 

 of the cell creeps upon it and remains there. This migration 

 of the chromatophores reminds of the migrations of the white 

 blood corpuscles. It is known that these blood corpuscles 

 show a chemical irritability, a chemotropism. It may be that 

 the chromatophores are also chemotropic, and that some of the 

 contents of the blood vessels attract the chromatophores, or 

 rather cause the protoplasma of the chromatophore to move 

 toward and upon the blood vessel. 



4. In order to find out whether the contents of the blood 

 vessels attract the chromatophores I made the following exper- 

 iment which is, perhaps, more interesting in itself than decisive 

 for our question. I made the embryo develop without the 

 heart-beat, to see if the migration of the chromatophores 

 to the blood vessels would take place even without the blood 

 circulating in the vessels. The embryo was put into sea water 

 which contained a specific heart-poison, namely, potassium chlo- 

 ride. Five gr. of this substance were added to 100 ccm. normal 

 sea water, after I had convinced myself that an addition of 3 

 gr. to 100 ccm. sea water is already sufficient to make the 

 heart of a Fundulus embryo stop beating in a few minutes. 

 The eggs segmented normally in a so strong solution of KCl, 

 and quite a number developed into a normal embryo. I found 

 it more favorable, however, to let the embryo first develop in 

 normal sea water, and not put it in the poisoned sea water for 



