CELL-LIiXEAGE 



other closely similar cells arc formed, just in front of them by 

 bjiddiug frojfi the iiiacroincrcs. These cells agree closel}' with 

 those derived from the " primary mesoblasts" both in size and 

 in the close reticulation and intensely chromatic character [of 



Fig. 3, Nereis. Sections of successive stages in the fomiation of the entoblast-phig 

 and mesoblast-bands in embryos of Nereis (actual sections, Flemming s fluid ; C is 

 tranverse, the others sagittal). Lettering as before. A shows a deep budding of 

 J/(cf. Fig. 2, B); B, later stage showing gioup of small cells [e^ derived from 

 M; C, still later stage, nearly transverse, showing the mesoblast-bands (///, w) 

 and the group of small cells {e) below; D, budding of the posterior macromere, 

 Z>; J5, recession of the entoblast-nuclei; JP, first appearance of the pigment in the 

 small cells. 



