Plate V. 

 Blastula, Gastrul.b, 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.) 



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



margin. 

 — Earl.v gastrula. The transverse shadow at the lower end of the germinal area represents 



the beginnings of the archenteric cavity. 



— Early gastrula, showing the extent of the archenteric space- 

 — 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. 

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

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

 — Gastrula, showing early eiubryo at a stage corresponding with Balfour's stage c in the 



shark. 

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

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



182 



