Bull. U. S. B. F., 191; 



Plate XVII. 



Fig. I. — ^Mature ovum, x 45. 



Fig. 2. — Ovum with early blastoderm, x 45: B, blastoderm. 

 Fig. 3, — Ovum with later blastoderm, x 45; C. cleavage cavity. 

 Fig. 4. — Ovum with blastodenn, showing embryonic shield, x 4: 

 ring. 



H5". embryonic shield; £.4.. embr>onic area; G" A', germ. 



