DEVELOPMENT OF DENTALIUM FOLLOWING REMOVAL OF D-QUADRANT BLASTOMERES AT SUCCESSIVE CLEAVAGE STAGES

Each primary micromere and macromere of the D-quadrant of Dentalium was deleted, through the mesentoblast stage, to investigate the way in which the polar lobe cytoplasm exerts its influence on development.-D and -1D embryos form an apical tuft but no posttrochal structures.-2D embryos form an apical tuft and a reduced posttrochal region without a shell. -3D and -4D are externally similar to control embryos. -1d embryos and -1c embryos have an apical tuft with a reduced number of cilia. Embryos in which both 1c and 1d are deleted lack the apical tuft.-2d embryos lack shell and most other posstrochal structures. -3d and-4d embryos appear externally equivalent to controls. The polar lobe cytoplasm exerts its influence sequentially, and as in Ilyanassa the maximal effect is at the third quartet stage. © 1979 Springer-Verlag.