The localization of morphogenetic factors in uncleaved eggs of Dentalium.

The effect of removing parts of unfertilized and fertilized eggs of Dentalium has been studied. Up to 70 % of the volume of a 1st polar lobe can be removed from the vegetal side of both unfertilized and fertilized eggs, without influencing apical tuft formation. The post-trochal region is reduced. These eggs form a reduced polar lobe at first cleavage. After removal of more than 70 % of the volume of a 1st polar lobe from the vegetal side of an uncleaved egg, before or after fertilization, no polar lobe is formed and larvae develop without apical tuft or post-trochal region. The polar lobe area is quantitatively determined in the uncleaved egg, but after fertilization of isolated vegetal fragments regulation occurs and the polar lobe becomes proportional in size to the fragment. Feulgen-positive granules, present at the vegetal side of the uncleaved egg, can be removed without influencing apical tuft formation. They may be important as determinants for the formation of the post-trochal region or adult structures.