ABSTRACT
The fertilized egg in which the germinal vesicle has disappeared shows a characteristic plasm distribution. A well defined cortical layer can be distinguished, free of yolk material and rich in pigment in the animal half of the egg, except for the animal pole region where the contents of the germinal vesicle have partially displaced the pigment. The plasm consists of a rather dense cytoplasm laden with very small yolk platelets and dispersed pigment granules. The inner animal plasm consists of cytoplasm heavily laden with mediumsize yolk platelets. The inner vegetative plasm is heavily laden with large yolk platelets. The fragmentation of the large egg cell starts with the first cleavage and extends over a considerable period of development. The epibolic extension of the animal area, as one of the aspects of the pregastrulation movements, leads to a displacement of the entire marginal zone towards the vegetative side.
