1 62 LOEB. [Vol. VIII. 



scattered chromatophores make their appearance. These chro- 

 matophores, the number of which increases steadily during the 

 next days, do not show any special arrangement except that 

 possibly their number is a little greater in those places where 

 the vitelline arteries leave the body, and at a little distance 

 from where the vitelline veins join the heart. There are two 

 kinds of chromatophores, one containing a red and the other a 

 black pigment, both sending out processes. 



The processes of the black cells are comparatively few in 

 number, whilst the red cells send out a much greater number of 

 small processes. At first one finds these cells scattered in the 

 lacunes between the yolk capillary vessels as well as spreading 

 out partly over a blood vessel. About the fourth or fifth day, 

 however, one can observe that many of the chromatophores 

 which are near a blood vessel send out one or more processes 

 on its surface. These processes follow the surface of the blood 

 vessel very closely, and by no means spread out over its other 

 side. This attachment to the surface of the blood vessel is 

 most striking in those places where the blood vessel undergoes 

 a bifurcation. Here the process of the chromatophore, rather 

 than leave the surface of the blood vessel, undergoes the same 

 bifurcation. This is at first more obvious in the black than in 

 the red chromatophores, the former on the whole appearing 

 more irritable. During the next days the number of chro- 

 matophores which send out processes to the blood vessels 

 increases and the whole mass of those which had already 

 stretched out their processes to a blood vessel creeps upon 

 the surface of the latter. The striking feature in the chro- 

 matophores after having reached the blood vessel is the change 

 in their dimensions. As a rule the diameter of a chromato- 

 phore before it comes in contact with a blood vessel is greater 

 in every direction than the diameter of a capillary blood vessel. 

 But as soon as it is on the blood vessel it stretches out in the 

 longtitudinal direction of the same in order to accommodate 

 its whole mass on its surface. At the point of bifurcation of 

 a blood vessel the chromatophore, as a rule, undergoes the 

 same bifurcation. By the ninth day practically every chro- 

 matophore has crept upon a blood vessel ; hardly a single 

 chromatophore can longer be found in the gaps between them. 



