Plate V. 

 Blastula, Gastrul.-K, and Early Embryos. 



(Preparations magnified about 15 diameters. In Figs. 30-34 the circumgerminal zone has been inaccurately litho- 

 graphed ; it should appear less conspicuous, its outer margin merging insensibly into the surrounding yolk.) 



Fig. 30. — Late blastula, showing especially the extent of the circumgerminal ring and its irregular 



margin. 

 Fig. 31. — Early gastrula. l"he transverse shadow at the lower end of the germinal area represents 



the beginnings of the archenteric cavity. 

 Fig. 32. — Early gastrula, showing the extent of the archenteric space. 

 Fig. 33. — Gastrula, showing the appearance of the head region of the embryo. In this preparation 



merocytes could be distinguished in the outer part of the circumgerminal ring. 

 Fig. 34. — Gastrula, showing the early embryo and the extent of the segmentation cavity. 

 Fig. 35. — Gastrula, slightly older, showing the early vascularization of the blastoderm. 

 Fig. 36. — Gastrula, showing early embryo at a stage corresponding with Balfour's stage c in the 



shark. 

 Fig. 37. — Blastoderm, showing embryo at a stage corresponding with Balfour's stage f in the shark. 

 Fig. 38. — Blastoderm and embryo at a stage corresponding with Balfour's stage g in the shark. 



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