Plate II. 

 Fig. 10. Primitive fuuiuliis stage. Transverse section tlirough the egg, 

 sliowing the manner in wliicli the mesoderm is formed, inscL, beneath tlie 

 blastopore, Mp. Tlie beginning of the endoderm is seen where a few cells 

 are being forced into the yolk, y. c 



Fig. 11. Blastodisc. Longitndinal section through egg, showing the 

 origin of the mesoderm by proliferation of cells from the ectoderm, ect., in 

 posterior, or caudal, region. 



Fig. 12. A similar- section a little to one side of the median line. 



Fig. 13. Cells from the blastodisc, showing the vesicular character of 

 their protoplasm. 



Fig. 14. Cells from the blastodisc, showing a nuclear spindle, n. sp., 

 which indicates the plane of division of the cells in this region. 



