Hemispheric-apex cells (HC), which are situated at the intersection of the three branches of Hoyle's organ inLoligo vulgarisandLoligo forbesiembryos, were investigated using light- and transmission-electron microscopy. The surface membrane of the HC exhibits many microvilli. Desmosomes between HC were distributed in patches along the plasma membrane. These desmosomes were also found between HC and the hatching enzyme producing cells of Hoyle's organ (CHO) and between neighbouring CHO. The area below the most apical desmosomes shows many cellular interdigitations. One (or several) small Golgi apparatus and many mitochondria were found in the cell centre. Mitochondria were also abundant in the most apical part of the cell. In the HC the nucleus is situated near the cell centre. The cell shape of the central part of the cell usually corresponds grossly to the nuclear form. Endoplasmic reticulum was found near the nucleus and in the lowermost part of the cell, but is never as abundant as in the CHO. In the most apical part of the HC many oval vesicles were found containing electron lucent material. Sagittal ultrathin sections showed that the tapering proximal part of the HC, directed toward the underlying tissue may end in a T-shaped form. As the HC and CHO degenerate after hatching, it is concluded that both structures are transient embryonic cells.