PLATE V. 

 BLASTULA, GASTRUL^, 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. The 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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