120 



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. 



