334 



GENERAL PRINCIPLES 



FIG. 204. FIG. 205. 



FIG. 204 is a cross section of the stage represented in Fig. 203. The medullary 

 plate is shown above, between entoderm and ectoderm. 



FIG. 205. A later larval stage showing six mesodermic pockets, and the 

 medullary plate completely covered by the ectoderm. 



FIG. 206. FIG. 207. 



FIG. 206 is a cross section through the anterior (left in the figure) end of the 

 stage represented by Fig. 205. 



FIG. 207 is a similar section through the posterior end of the same stage. In 

 both figures the medullary groove, the mesodermic somites and the first steps 

 in the formation of the notochord are shown. 



