540 



CHARLES R. STOCKARD 



Fig. 10 A camera sketch of an entire embryo of 76 hours except the anterior 

 end of the head. The mesenchymal cells wandering away from the tail region and 

 to a less degree from the sides of the body. 



DEVELOPMENT AND DIFFERENTIATION OF THE WANDERING CELLS 



1 . Chromatophores 



a. The black type of chromatophore. The first to be considered 

 of the four types of cells which develop on the yolk-sac are 

 the black chromatophores. These are the largest and most con- 

 spicuous cells of the yolk-sac. In the early stages discussed 

 above, one notes even in embryos of 2 days that certain cells 

 of the yolk mesenchyme are considerably larger than others. 



