1. The structure of the egg is described.

  2. Segmentation of the egg is followed from the eight-celled stage up to the formation of the blastoderm. A migration of blastomeres from one pole of the egg towards the opposite has been observed and in the course of this migration a circle of 10-11 cells moves in front of the others.

  3. Gastrulation takes place by immigration. A V-shaped mesodermal headband is differentiated which gives rise to the rudiments of the naupliar appendages after gastrulation is completed.

  4. The entire post-naupliar region of the body is formed by the activity of ectodermal and mesodermal teloblasts. No caudal furrow is formed.

  5. The gut is ectodermal, formed by the union of the stomodoeum and a long proctodoeum.

  6. An ectodermal dorsal organ forms in early development and persists throughout embryonic life. The pre-antennulary mesodermal strands become attached to this organ.

  7. The origin, development, and derivatives of the pre-antennulary mesodermal somites are described.

  8. The origin of the liver is traced from the naupliar mesoderm. The probability that the liver plays an important part in yolk absorption is discussed.

  9. The development of the trunk mesoderm and an early grouping of cells into segmental and intersegmental regions are described.

  10. The formation of the heart, pericardium, and dorsal aorta is described.

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