The Movement of the Egg Nucleus in Relation to the Sperm Aster in the Echinoderm Egg

Abstract

The observations described in this paper indicate that the sperm nucleus is carried to the centre of the egg by the progressive enlargement of a gelated body, the sperm aster, and that the egg nucleus is carried to the sperm nucleus by a centripetal cytoplasmic flow directed toward the astral lake, within which the sperm nucleus lies. The curved path which the egg nucleus describes results from the continued change in direction of a cytoplasmic flow streaming toward the moving astral lake. The egg nucleus, when within the aster, is not only carried towards the lake by cytoplasmic streaming, but it is also moved centrally by the migration of the sperm aster toward the approximate centre of the egg.