FORMATION OF THE LAYERS. 



273 



FIG. 2. 



Diagrammatic longitudinal sections of embryo, which develops in the same manner as 

 the Elasmobranch embryo, but in which 'the ovum contains far less food-yolk 

 than is the case with the Elasmobranch ovum. 



Epiblast without shading. Mesoblast black with clear outlines to the cells. Lower 

 layer cells and hypoblast with simple shading. 



ep. epiblast. m. mesoblast. hy. hypoblast. sg. segmentation cavity. al. 

 alimentary cavity. nc. neural canal, hf. head-fold. . nuclei of the yolk. 

 The stages A , B and C are the same as in figure . 



