Series F, 1 and 2. Sections through a blastoderm with primitive groove.
1. Section shewing a deep pit in front of primitive streak, probably an early indication of the neurenteric canal. 2. Section immediately following 1.
Fig. G. Section through blastoderm with well-developed primitive streak, shewing an exceptionally deep slit-like primitive groove.
Series H, 1 and 2. Sections through a blastoderm with a fully-developed primitive streak.
1. Section through the anterior part of area pellucida, shewing the cubical granular hypoblast cells in this region. 2. Section slightly behind 1, shewing the primitive hypoblast cells differentiated into stellate cells, which can hardly be resolved in the middle line into hypoblast and mesoblast.
Series I, 1, 2, 3, 4 and 5. Sections through blastoderm somewhat older than Series H.
1. Section through area pellucida well in front of primitive streak. 2. Section through area pellucida just in front of primitive streak. 3. Section through the front end of primitive streak. 4. Section slightly behind 3. 5. Section slightly behind 4.
Series K, 1, 2, 3, 4 and 5. Sections through a blastoderm in which the first traces of notochord and medullary groove have made their appearance. Rather more than half the section is represented in each figure, but the right half is represented in 1 and 3, and the left in 2 and 4.
1. Section through notochord immediately behind the head fold. 2. Section shewing medullary groove a little behind 1. 3. Section just in front of the primitive streak. 4 and 5. Sections through the front end of the primitive streak.